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
- Switch to using sphinx-build; fix build warnings
- Cleanup doc/source/conf.py to remove now obsolete content.
- Use newer openstackdocstheme version
- Raise oslo.utils version, 3.36.5 introduced uuidsentinel.
Change-Id: I8c81e0c1944c239e460befbf886993270902ee04
a98989b2ef