This repo is now testing only with Python 3, so let's make
a few cleanups:
- Remove python 2.7 stanza from setup.py
- Add requires on python >= 3.6 to setup.cfg so that pypi and pip
know about the requirement
- Remove obsolete sections from setup.cfg
- Update classifiers
- Update requirements, no need for python_version anymore
- Cleanup */source/conf.py to remove now obsolete content.
- Use newer openstackdocstheme, reno, Sphinx, hacking versions
for python3
- Add pytest as requirement, horizon does not provide this anymore and
the tests here call horizon files that need it.
Change-Id: I5983a19cadb210d55c30107fb963cfeaae0f1ee9
805d94e985