Use the new PTI docs building commands, these use "tox -e docs" for
building, also update the publishing job.
Update tox.ini to use sphinx-build directly as documented in the PTI.
Note that we have to disable warnings, otherwise building fails with:
doc/source/results/ocata/ptl.rst:3:Duplicate explicit target name: "tony breeds (tonyb)".
Be aware that with current pbr and Sphinx, warnings are disabled due to
change of parameter names - so, this keeps the status quo.
Depends-On: https://review.openstack.org/615501
Needed-By: https://review.openstack.org/615637
Change-Id: I4713f3a25e08056b7bce9812fa2cf62119330fcc
79cc6c1db5