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: I3dadeaa3242d0b55ba891a8eb4abb199a8d2468b

The v1 has officially been removed from Designate since
the Queens release, and was deperecated long before that.

Change-Id: Ic5b44761ff939e2b319924af87849b3a79f9cb07

As keystoneclient's Session and auth plugins have been deprecated in
favor of keystoneauth, the documentation examples must reflect that.

This patch updates all examples in order to show keystoneauth Session
usage instead of deprecated keystoneclient Session. Also, the python API
bindings were updated too.

Change-Id: I4b64fee4f526cc5b4a5e36cc8edb61164ceded51

Replaced print in python 2 to print() to provide py 2/3 compatibility

Change-Id: I805ecdbdd07ea89c1595c045fc5b380f9bb42335

This provides bindings for:

- zones
- recordsets
- tlds
- blacklists
- limits
- nameservers

With associated unit tests.

Change-Id: Ie9b79340bd327b78916fd038633842da3ace881b