Fix Sphinx 6.0 doc build error.

Change-Id: I9a1571cf416d32d040d8ff05d1c8b1769d1d0558

Change-Id: I59e8ae94eb83ae3a1ddcc99091e53686d2d55186

This library no longer supports Python 2, thus usage of six can be
removed. This also removes workaround about pickle library used in
Python 2 only.

Change-Id: I19d298cf0f402d65f0b142dea0bf35cf992332a9

Change-Id: I47faea9b3c0324d3860a5209d521bc76de03bc47

Introduced changes:
- pre-commit config and rules.
- Add pre-commit to pep8 gate, Flake8 is covered in the pre-commit hooks.
- Applying fixes for pre-commit compliance in all code.

Also commit hash will be used instead of version tags in pre-commit to
prevend arbitrary code from running in developer's machines.

pre-commit will be used to:
- trailing whitespace;
- Replaces or checks mixed line ending (mixed-line-ending);
- Forbid files which have a UTF-8 byte-order marker
  (check-byte-order-marker);
- Checks that non-binary executables have a proper
  shebang (check-executables-have-shebangs);
- Check for files that contain merge conflict strings
  (check-merge-conflict);
- Check for debugger imports and py37+ breakpoint()
  calls in python source (debug-statements);
- Attempts to load all yaml files to verify syntax (check-yaml);
- Run flake8 checks (flake8) (local)

For further details about tests please refer to:
https://github.com/pre-commit/pre-commit-hooks

Change-Id: I3640bb690c552a428ae0e8250adffbc3a51a310e
Signed-off-by: Moisés Guimarães de Medeiros <moguimar@redhat.com>

Switch to openstackdocstheme 2.2.1 and reno 3.1.0 versions. Using
these versions will allow especially:
* Linking from HTML to PDF document
* Allow parallel building of documents
* Fix some rendering problems

Update Sphinx version as well.

Disable openstackdocs_auto_name to use 'project' variable as name.

Change pygments_style to 'native' since old theme version always used
'native' and the theme now respects the setting and using 'sphinx' can
lead to some strange rendering.

Remove docs requirements from lower-constraints, they are not needed
during install or test but only for docs building.

openstackdocstheme renames some variables, so follow the renames
before the next release removes them. A couple of variables are also
not needed anymore, remove them.

See also
http://lists.openstack.org/pipermail/openstack-discuss/2020-May/014971.html

Change-Id: Ieb7ce05f6611ad743336a35065402888176c7de3

Change-Id: Ie42f30fa22c0d9864e355c4037520bcca3747a76

OpenStack is dropping the py2.7 support in ussuri cycle.

Complete discussion & schedule can be found in
- http://lists.openstack.org/pipermail/openstack-discuss/2019-October/010142.html
- https://etherpad.openstack.org/p/drop-python2-support

Ussuri Communtiy-wide goal:
https://governance.openstack.org/tc/goals/selected/ussuri/drop-py27.html

Remove cruft from setup.cfg.
Update hacking so that it works with python3 and silence new warnings.

Change-Id: Id224fc09ac36d2a84e82347530bb5e5d30665803

Change-Id: Ie9f1ca14eed287f3c25553d029d4a4b2ca5274d0

Sphinx 2.0 no longer works on python 2.7, so we need to start capping it
there. We remove Sphinx and doc8 from the 'test-requirements.txt' file
and '[extra] test' section in 'setup.cfg' since none of our tests
actually use this. Finally, we remove a number of dependencies from
'doc/requirements.txt' since these were already specified in
'test-requirements.txt' and we install these as part of the tox target.

Change-Id: I3981f47f4278f726e3c078723f90d4b9ba1699a6
Signed-off-by: Stephen Finucane <sfinucan@redhat.com>