add glusterfs epel repo to EL6 config

To ensure that we include glusterfs since vdsm now depends on it.
Include the repos because we don't want to have to maintain all the
gluster updates on ovirt.org.

Note:  Fedora gets the updates automatically

Change-Id: I89bb7e231d45579f7e72f8e085798d2680b287e5
Signed-off-by: Mike Burns <mburns@redhat.com>