Catch gluster import error in glusterVolume

glusterSD is imported by hsm and imports glusterVolume. with_gluster=0
variable leaves gluster files but omit gluster directory. This leads to
import error that must be treated.

Change-Id: I6abf41add3b83336f2e90139bc6752f8e9446960
Signed-off-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/21625
Reviewed-by: Dan Kenigsberg <danken@redhat.com>