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: I91036721fcb78c8eec234577d3c4f40690fb6eb6

callback_plugins/validation_json.py

@@ -13,8 +13,6 @@
 # implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-
-from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type
 
 import datetime

callback_plugins/validation_output.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 pprint
 
 from ansible import constants as C

library/docker_facts.py

@@ -13,10 +13,6 @@
 # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 # License for the specific language governing permissions and limitations
 # under the License.
-
-from __future__ import absolute_import
-from __future__ import division
-from __future__ import print_function
 import itertools
 
 from ansible.module_utils.basic import AnsibleModule

scripts/tripleo-ansible-inventory

@@ -19,8 +19,6 @@
 # TODO(mandre)
 # If possible get info from ironic for hosts prior to deployment
 
-from __future__ import print_function
-
 import json
 import os
 import sys

tripleo_validations/utils.py

@@ -14,8 +14,6 @@
 # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 # License for the specific language governing permissions and limitations
 # under the License.
-
-from __future__ import print_function
 from six import string_types
 
 import collections