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: I2cf7495c5cb42c632993bb2372ffb626ab97bf0d

container_config_scripts/nova_statedir_ownership.py

@@ -13,7 +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 print_function
 import logging
 import os
 import pwd

container_config_scripts/placement_wait_for_service.py

@@ -17,8 +17,6 @@
 # shell script to check if placement API is up after X attempts.
 # Default max is 60 iterations with 10s (default) timeout in between.
 
-from __future__ import print_function
-
 import logging
 import os
 import re

deployed-server/scripts/enable-ssh-admin.sh

@@ -23,7 +23,6 @@ function get_python() {
 
 function overcloud_ssh_hosts_json {
     echo "$OVERCLOUD_HOSTS" | $(get_python) -c '
-from __future__ import print_function
 import json, re, sys
 print(json.dumps(re.split("\s+", sys.stdin.read().strip())))'
 }

network/endpoints/build_endpoint_map.py

@@ -22,8 +22,6 @@ The --check option verifies that the current output file is up-to-date with the
 latest data in the input file. The script exits with status code 2 if a
 mismatch is detected.
 """
-
-from __future__ import print_function
 import collections
 import copy
 import itertools