The default nodeset was just changed to focal [1], which in the absence
of the python-is-python3 package doesn't provide a python binary.
Enable again the docker-build and docker-publish Zuul jobs.
[1] https://review.opendev.org/c/opendev/base-jobs/+/789098
Change-Id: Ic78169052517701b235e906852923388d93776e8
Used to be: git.openstack.org/openstack/monasca-persister?h=stable/pike
Now : opendev.org/openstack/monasca-persister/src/branch/stable/pike
Since the way links to specific branches changed, usage of
those links has to be changed as well.
CONSTRAINTS_BRANCH variable was removed because CONSTRAINTS_FILE
contains link to the upper-requirements file with specified branch.
Story: 2005666
Task: 30967
Depends-On: https://review.opendev.org/#/c/659073/
Change-Id: I444e7c43ab52206d433cb20339ddf0caecaba61a
Pierre Riteau