CBQE-0 :: fix graceful failover vbucket distribution checks

Change-Id: I57b89ba7c2a8c482d5cc56c5e213ffc472aa4d1c
Reviewed-on: http://review.couchbase.org/40348
Reviewed-by: Parag Agarwal <agarwal.parag@gmail.com>
Tested-by: Parag Agarwal <agarwal.parag@gmail.com>