Switch to new build-openstack-docs-pti template, this runs "tox -e cover". Update tox.ini so that it continues to use python3. Change-Id: I2dcea4a954b2ae16c778163e7782216041efb3cf
Depends-On: https://review.openstack.org/573460 Change-Id: I91b626bf84d63a2b5da311319a55f165f738a95e