CBQE-0: fix for rebalance exception is not propogated and validation continues after rebalance failure

Change-Id: I0817ed17b3a7cdf2a327c0329dd564b98fcdaee6
Reviewed-on: http://review.couchbase.org/37698
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Parag Agarwal <agarwal.parag@gmail.com>
Tested-by: Parag Agarwal <agarwal.parag@gmail.com>