engine:Fixed error message Add/remove/update Gluster Hook

proper vdsname is substituted in 'server not up'
error message of Gluster Hook resolve conflicts popup

Change-Id: If018578d2fe89f9ed10dad948b7bd922033c78e1
Bug-Url: https://bugzilla.redhat.com/977355
Signed-off-by: Karnan TC <kchidamb@redhat.com>