fileSD: include gluster in getMountsList

It is not exactly clear what previous change broke scanDomains but
looking at the code it seems that gluster was never explicitly handled.

This patch adds the explicit support for gluster in scanDomains fixing
the problem of missing storage domain links in the pool directory.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1116585
Change-Id: I81600a68bbea99c1079bf153cf2c105c6fe73f70
Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/30934
Reviewed-by: Dan Kenigsberg <danken@redhat.com>