CBQE-0: fix for failover/rebalance - queue empty and active=replica items, graceful failover as default, ops running during failover

Change-Id: Ia0ed34f3a722ea70a31fd9472921e55c60ee44ee
Reviewed-on: http://review.couchbase.org/36725
Reviewed-by: Parag Agarwal <agarwal.parag@gmail.com>
Tested-by: Parag Agarwal <agarwal.parag@gmail.com>