fix storage.fuser

Bug-Url: https://bugzilla.redhat.com/922515
Change-Id: Iabd58847db7090f83106d30a763d09c0a7b78741
Signed-off-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/13302
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Tested-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/13303
Reviewed-by: Federico Simoncelli <fsimonce@redhat.com>