OpenStack is dropping the py2.7 support in ussuri cycle.
Make a few cleanups:
- Remove python 2.7 stanza from setup.py
- Add python-requires to setup.cfg so that pypi and pip know
about support Python version
- Remove ancient sections from setup.cfg
- Remove version_info setting from conf.py, openstackdocstheme does this
automatically nowadays.
Change-Id: I5b9c159752c932f874015f20822862c70562c2bd
f01a0f336c