switch documentation job to new PTI
switch documentation job to new PTI

This is a mechanically generated patch to switch the documentation
jobs to use the new PTI versions of the jobs as part of the
python3-first goal.

See the python3-first goal document for details:
https://governance.openstack.org/tc/goals/stein/python3-first.html

Change-Id: I8721027b63bc835185251b08c17b0e6ae3911cd8
Story: #2003250

openstack-dev/pbr,openstack-dev/pbr,openstack-dev/pbr