CBQE-1691: updated rebalance xdcr async_rebalance_out test to verify
MB-9497

Change-Id: Ie2e7a1db4ac7b6ad3eeb732d9732a7a3a22dd5f5
Reviewed-on: http://review.couchbase.org/33069
Reviewed-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>
Tested-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>