Voluptuous is a transitive test requirement and latest breaks on py27
due to enum not being importable. Address this by capping Voluptuous on
python27.
Change-Id: I4301557247a447d0c0271474fc21cf9c6a1c5c4a
Sphinx<2 is required for python2 now. This is copied from the
OpenStack requirements file under the assumption the good versions
have been worked out there.
Change-Id: I5df018b89680b236840a915384cd8341081991bc
Depends-On: https://review.opendev.org/667228
Oslosphinx seems to no longer work and is breaking our docs builds.
Switch to openstackdocstheme instead.
Change-Id: I72600ce84cb04bfa8350b273c030ae3914f7de40