Establish nightly test runs with Samba and Gluster release versions/branches (instead of master branches)

We want to be testing samba and Gluster released versions and/or release branch heads against one another. Gluster is already building release versions into RPMs. For Samba, this has to be added (separate issue). Mainly interested in

* latest release versions
* release version combinations used in d/s Red Hat Gluster storage 