Cleanup requirement and set ignore_basepython_conflict = True
in tox to avoid python version conflict warning which going
to be error in future.

Change-Id: Iae7e0bb9e8af52ec3aafba7508305d8692d3c762

2020 is coming, everyone should be using Python 3 now.

As per the official python support timeline set forth by the OpenStack
TC [1], OpenStack Train (in our case, kolla-ansible 9.x) is the last
release that will support python2.7.

[1] https://governance.openstack.org/tc/resolutions/20180529-python2-deprecation-timeline.html

Implements: blueprint drop-py2-support

Change-Id: Ibb3b12a779ecfd424053d0b3e98dac2f21d909bc

Sphinx 1.8 introduced [1] the '--keep-going' argument which, as its name
suggests, keeps the build running when it encounters non-fatal errors.
This is exceptionally useful in avoiding a continuous edit-build loop
when undertaking large doc reworks where multiple errors may be
introduced.

[1] https://github.com/sphinx-doc/sphinx/commit/e3483e9b045

Change-Id: I405812a0039274139e055c54ab7b451dc753c842

The is one of community goals that each project should produce a
single PDF file. The pdf should be in the output of openstack-tox-docs
job.

TeX packages are required to build PDF locally, following is
recommended:

* inkscape
* texlive-latex-base
* texlive-latex-extra
* texlive-fonts-recommended

More about the goal:
https://governance.openstack.org/tc/goals/train/pdf-doc-generation.html
https://etherpad.openstack.org/p/train-pdf-support-goal
https://etherpad.openstack.org/p/pdf-goal-train-common-problems

Change-Id: Ia0f8b73bcbda6295319f5c8de1aa02a40844207b

1. Update the UPPER_CONSTRAINTS_FILE to releases.openstack.org[1]
2. Blacklist sphinx 2.1.0[2]

[1]: http://lists.openstack.org/pipermail/openstack-discuss/2019-May/006478.html
[2]: https://github.com/sphinx-doc/sphinx/issues/6440

Change-Id: Ie5f9ae1bd5c45617c6b7fde0e490d471e172c24e

Depends-On: https://review.opendev.org/662209


Co-authored-by: Stephen Finucane <stephenfin@redhat.com>
Closes-Bug: #1830586
Change-Id: I48d3f4c5f7c04b1ab41b3bad2a6c19e1e9a218fd

For compliance with the Project Testing Interface [1]
as described in [2]

[1]
https://governance.openstack.org/tc/reference/project-testing-interface.html
[2]
http://lists.openstack.org/pipermail/openstack-dev/2017-December/125710.html

doc8 command is dropped from docs tox envs.
So this affect nothing and run in PEP8.

Related-Bug: #1765348

Depends-On: Icc7fe3a8f9716281de88825e9d5b2fd84de3d00a
Change-Id: Idf9a16111479ccc64004eac9508da575822a3df5