Cleanup doc/requirements to just use what is needed for doc building.
Move reno to doc/requirements, add doc8 to test-requirements.
update tox.ini:
* doc8 should be in pep8 as linter and not docs according to PTI [1]
* Only build main doc in docs environment, CI uses this and we waste
just time building api-ref as well, there's a separate environment for
this. This follows PTI [1]
* Do not include requirements file for docs building, it's not needed
with apidoc.
* Use common deps for all docs build environments.
Cleanup doc/source/conf.py, with the switch to api-doc a lot of settings
are not needed anymore, also the eventlet bug is fixed.
Update openstackdocstheme to 1.20.0 and which allows to remove obsolete
setting of html_last_updated_fmt, project, latex_elements from conf.py.
Add doc8 to lower-constraints to make requirments-check happy.
[1] https://governance.openstack.org/tc/reference/project-testing-interface.html#documentation
Change-Id: If86dd619402495d9d4470b14cb270fcf53db6794
af04cc3392