webadmin: gluster volume rebalance status popup

Added a new action 'Status' under the 'Rebalance' actions group.
On clicking the 'Status' action 'Rebalance Status' popup for
the selected gluster volume will be shown.

Change-Id: I0d1f63b21dfbed88fa2b4e8c077e3e5e54ba7b09
Signed-off-by: Kanagaraj M <kmayilsa@redhat.com>
Signed-off-by: Anmol Babu <anbabu@redhat.com>