gluster: Fix rebalance message to display volume name along with confirmation

Change the text as "Are you sure you want to stop the rebalance operation
on the volume : <volume-name>?"

Change-Id: Ic23df363c3627f9143971b6d9257f1e54b5593ba
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1021343
Signed-off-by: Timothy Asir <tjeyasin@redhat.com>