CBQE-0:stop rebalance before cleaning up cluster

Change-Id: I141a93f0d40d2be1ec407c674ebd1b504fcab39f
Reviewed-on: http://review.couchbase.org/30956
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>