CBQE-0: stop rebalance in teardown

Change-Id: Ic85821eeeac68983d2f5fe3d47ce8014eedffd36
Reviewed-on: http://review.couchbase.org/30880
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>