removing requirement on vdsm-gluster

The use the hosted engine setup does in gluster doesn't require the
vdsm-gluster RPM, as the functionality of creating storage domains
exists in the core of VDSM (vdsm-gluster is adding functionality to
create gluster bricks and volumes, which isn't required here).

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1001161
Change-Id: I40722917a3ed4b51bf16db480c8d98fb3ff8d6ed
Signed-off-by: Oved Ourfali <oourfali@redhat.com>