Stop to use the __future__ module.

The __future__ module [1] was used in this context to ensure compatibility
between python 2 and python 3.

We previously dropped the support of python 2.7 [2] and now we only support
python 3 so we don't need to continue to use this module and the imports
listed below.

Imports commonly used and their related PEPs:
- `division` is related to PEP 238 [3]
- `print_function` is related to PEP 3105 [4]
- `unicode_literals` is related to PEP 3112 [5]
- `with_statement` is related to PEP 343 [6]
- `absolute_import` is related to PEP 328 [7]

[1] https://docs.python.org/3/library/__future__.html
[2] https://governance.openstack.org/tc/goals/selected/ussuri/drop-py27.html
[3] https://www.python.org/dev/peps/pep-0238
[4] https://www.python.org/dev/peps/pep-3105
[5] https://www.python.org/dev/peps/pep-3112
[6] https://www.python.org/dev/peps/pep-0343
[7] https://www.python.org/dev/peps/pep-0328

Change-Id: Ieccdcdcec557efe480dcf3546299718b0baa37a4

os_ken/app/simple_switch_snort.py

@@ -13,8 +13,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
-
 import array
 
 from os_ken.base import app_manager

os_ken/cmd/of_config_cli.py

@@ -23,8 +23,6 @@
 #      --peers=sw1=localhost:1830:username:password
 #     (Cmd) raw_get sw1
 
-from __future__ import print_function
-
 import cmd
 import sys
 

os_ken/cmd/rpc_cli.py

@@ -29,8 +29,6 @@
 #     NOTIFICATION from echo-server ['notify-method', ['param1', 'param2']]
 #     (Cmd)
 
-from __future__ import print_function
-
 import ast
 import cmd
 import signal

os_ken/lib/ovs/vsctl.py

@@ -18,8 +18,6 @@
 ``ovs-vsctl`` command like library to speak OVSDB protocol
 """
 
-from __future__ import print_function
-
 import logging
 import operator
 import os

os_ken/lib/stringify.py

@@ -14,8 +14,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
-
 import base64
 import inspect
 

os_ken/log.py

@@ -13,8 +13,6 @@
 # implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-
-from __future__ import print_function
 from os_ken import cfg
 import inspect
 import platform

os_ken/services/protocols/bgp/api/all.py

@@ -1,7 +1,5 @@
 # flake8: noqa
 
-from __future__ import absolute_import
-
 from . import core
 from . import operator
 from . import prefix

os_ken/services/protocols/bgp/api/base.py

@@ -18,7 +18,6 @@
 
  This API can be used by various services like RPC, CLI, IoC, etc.
 """
-from __future__ import absolute_import
 
 import logging
 import traceback

os_ken/services/protocols/bgp/base.py

@@ -15,7 +15,6 @@
 """
   Defines some base class related to managing green threads.
 """
-from __future__ import absolute_import
 
 import abc
 from collections import OrderedDict

os_ken/services/protocols/bgp/bgp_sample_conf.py

@@ -1,6 +1,4 @@
 
-from __future__ import absolute_import
-
 import os
 
 from os_ken.services.protocols.bgp.bgpspeaker import RF_VPN_V4

os_ken/services/protocols/bgp/core_managers/__init__.py

@@ -13,8 +13,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import absolute_import
-
 from .configuration_manager import ConfigurationManager
 from .import_map_manager import ImportMapManager
 from .peer_manager import PeerManager

os_ken/services/protocols/bgp/operator/commands/show/rib.py

@@ -1,4 +1,3 @@
-from __future__ import absolute_import
 
 from os_ken.services.protocols.bgp.base import ActivityException
 from os_ken.services.protocols.bgp.operator.command import Command

os_ken/services/protocols/bgp/operator/commands/show/vrf.py

@@ -1,4 +1,3 @@
-from __future__ import absolute_import
 
 import logging
 import pprint

os_ken/services/protocols/zebra/db/__init__.py

@@ -17,8 +17,6 @@
 Database implementation for Zebra protocol service.
 """
 
-from __future__ import absolute_import
-
 from sqlalchemy import create_engine
 from sqlalchemy.orm import sessionmaker
 

os_ken/services/protocols/zebra/db/base.py

@@ -13,8 +13,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import absolute_import
-
 import functools
 import logging
 

os_ken/services/protocols/zebra/db/interface.py

@@ -13,8 +13,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import absolute_import
-
 import logging
 
 from sqlalchemy import Column

os_ken/services/protocols/zebra/db/route.py

@@ -13,8 +13,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import absolute_import
-
 import logging
 import socket
 

os_ken/tests/integrated/bgp/base.py

@@ -14,8 +14,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import absolute_import
-
 import logging
 import sys
 import unittest

os_ken/tests/integrated/bgp/base_ip6.py

@@ -14,8 +14,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import absolute_import
-
 import logging
 import sys
 import unittest

os_ken/tests/integrated/bgp/test_basic.py

@@ -14,8 +14,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import absolute_import
-
 import time
 
 from os_ken.tests.integrated.common import docker_base as ctn_base

os_ken/tests/integrated/bgp/test_ip6_basic.py

@@ -14,8 +14,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import absolute_import
-
 import time
 
 from os_ken.tests.integrated.common import docker_base as ctn_base

os_ken/tests/integrated/common/docker_base.py

@@ -16,8 +16,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import absolute_import
-
 import itertools
 import logging
 import os

os_ken/tests/integrated/common/oskenbgp.py

@@ -13,8 +13,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import absolute_import
-
 import logging
 import os
 import time

os_ken/tests/integrated/common/quagga.py

@@ -16,8 +16,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import absolute_import
-
 import logging
 import os
 

os_ken/tests/integrated/run_test.py

@@ -14,8 +14,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import absolute_import
-
 import logging
 import os
 import sys

os_ken/tests/integrated/run_tests_with_ovs12.py

@@ -14,8 +14,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
-
 import unittest
 from nose.tools import ok_, eq_, timed, nottest
 

os_ken/tests/integrated/test_of_config.py

@@ -110,8 +110,6 @@ Here is my sys.config used for this test.
 
 """
 
-from __future__ import print_function
-
 import traceback
 
 import lxml.etree

os_ken/tests/integrated/vrrp_common.py

@@ -14,8 +14,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
-
 import time
 import random
 

os_ken/tests/packet_data_generator3/gen.py

@@ -1,7 +1,5 @@
 #! /usr/bin/env python
 
-from __future__ import print_function
-
 import getopt
 import os
 import re

os_ken/tests/unit/__init__.py

@@ -1,4 +1,3 @@
-from __future__ import absolute_import
 
 # Note: The following import statement is defined in order to resolve
 # the conflict of the module names between 'os_ken.lib.ovs' and 'ovs'.

os_ken/tests/unit/ofproto/test_parser.py

@@ -14,8 +14,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
-
 import six
 import sys
 import unittest

os_ken/tests/unit/ofproto/test_parser_compat.py

@@ -14,8 +14,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
-
 import six
 import sys
 import unittest

os_ken/tests/unit/ofproto/test_parser_ofpmatch.py

@@ -14,8 +14,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
-
 try:
     # Python 3
     from functools import reduce

os_ken/tests/unit/packet/test_bgp.py

@@ -14,8 +14,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
-
 import logging
 import os
 import sys

os_ken/tests/unit/packet/test_geneve.py

@@ -13,8 +13,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
-
 import logging
 import os
 import sys

os_ken/tests/unit/packet/test_gre.py

@@ -13,8 +13,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
-
 import logging
 import os
 import sys

os_ken/tests/unit/packet/test_openflow.py

@@ -13,8 +13,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
-
 import logging
 import os
 import sys

os_ken/tests/unit/packet/test_vrrp.py

@@ -16,8 +16,6 @@
 
 # vim: tabstop=4 shiftwidth=4 softtabstop=4
 
-from __future__ import print_function
-
 import unittest
 import logging
 import six

os_ken/tests/unit/packet/test_zebra.py

@@ -13,8 +13,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
-
 import os
 import socket
 import sys