engine: Fix for return value issue in StopRebalanceGlusterVolumeCommand

   Discarding the status values returned from StopRebalance command as it
has issue during deserialization. Also the return value is no where used.

Change-Id: I90ec8b8495ede37a1dc6b8929cf80b445598a234
Signed-off-by: Ramesh Nachimuthu <rnachimu@redhat.com>