switch release job to python 3
switch release job to python 3

This is a mechanically generated patch to switch the release
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: I016721d52ced46c74bf28212d8b7edadc4967eab
Story: #2002586
Task: #24296

openstack/freezer-api,openstack/freezer-api,openstack/freezer-api,openstack/freezer-api