CBQE-0: fix test case hanging due to rebalance failure

Change-Id: I4c176af313e0c65f6231f24937991f86c875bcd6
Reviewed-on: http://review.couchbase.org/36763
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Parag Agarwal <agarwal.parag@gmail.com>
Tested-by: Parag Agarwal <agarwal.parag@gmail.com>