Cinder-CI: Run GlusterFS-Cinder CI job for master and n-1 releases only

[Deepak C Shetty]

Cinder-GlusterFS CI job currently fails for stable/kilo
See : https://review.openstack.org/#/q/status:open+project:openstack/cinder+branch:stable/kilo,n,z

When the CI job was developed/added, it was primarily for the then master (Now Liberty, which is stable/liberty) only.

There was a concern noted in https://review.openstack.org/#/c/240412/ about this job failing always for stable/kilo,
which is a valid concern.

Current plan (unless otherwise noted in future comments) is to support Cinder-GlusterFS CI job for Mitaka and Liberty
releases (IOW, current and n-1 only)

That would mean we need to stop Cinder-GlusterFS CI job for n-2 (Kilo) and beyond, hence this bug.