Check devstack-gate changes on stable branch jobs

Since openstack-infra/devstack-gate only has a master branch,
changes to it did not previously get tested against stable branches
of devstack and tempest and the integrated projects. Reduce this
asymmetry by adding non-voting versions of those jobs with
appropriate overrides forcing use of the target stable branches.

* .../jenkins_job_builder/config/devstack-gate.yaml: Add templates
for the stable branch override check jobs which are also running on
master, and direct jobs for those which were removed after grizzly.

* .../jenkins_job_builder/config/projects.yaml: Apply release names
to expand the new job templates. Jobs for grizzly which will also
appear in havana have their templates pre-filled for the upcoming
release, but note that there are also several post-grizzly jobs
which will need templates too when the time comes.

* .../zuul/layout.yaml: Add the new folsom and grizzly jobs to the
devstack-gate project's check pipeline.

Change-Id: I487438cdde84b57d338893800e91bfccd6e49d0a
Merge "Check devstack-gate changes on stable branch jobs"