Fixing vdsm builds

There were two issues:

* Gluster repos not being set on el6-ovirt3.5
* Avoiding runnin fc19 mock jobs on fc21 hosts (yum conflicts BZ:1156497)

Change-Id: I782848a7d848cd3e74b7755c144a0170cf26efe6
Signed-off-by: David Caro <dcaroest@redhat.com>