MB-100: changes in start_stop_rebalance_in_out

for mixed cluster run

Change-Id: I3606687b62afe044a5d8d2d25601b81521d728c8
Reviewed-on: http://review.couchbase.org/24466
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>