CBQE-0: fix rebalance tests

Change-Id: I7e7a47559dbf4389048b050d478763d922b7cfe9
Reviewed-on: http://review.couchbase.org/29979
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>