cli: Fixing ambiguous message error for rebalance <volname> start command

Previously output message of command 'gluster volume rebalance <volname>
start/start force/fix-layout start' was ambiguous and poorly formatted.
Previously output message was: "volume rebalance: <volname>: success:
Starting rebalance on volume <volname> has been successful."

Now with this fix properly formatted output message is:
"volume rebalance: <volname>: success: Rebalance on <volname> has been
started Successfully. Use rebalance status command to check status of
the rebalance process."

Change-Id: I23268fc13b05d1b39ffe4c702d0e4f73085acd1c
BUG: 1087487
Signed-off-by: ggarg <ggarg@redhat.com>
Reviewed-on: http://review.gluster.org/7473
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>