webadmin: removed volume rebalance actions

Gluster Volume Rebalance feature is not fully implemented
in ovirt-engine-3.3. Removing the actions for now

Change-Id: I0768d48f432235f405e9a6d8fee36794e2a72628
Bug-Url: https://bugzilla.redhat.com/1046000
Signed-off-by: Kanagaraj M <kmayilsa@redhat.com>