CBQE-0 :: Generalize setting of flow_control and add parameter for verify_max_unacked_bytes

Change-Id: Idea2168854b494ec990ef8e8a3f1138dbeb80e9a
Reviewed-on: http://review.couchbase.org/37993
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Parag Agarwal <agarwal.parag@gmail.com>
Tested-by: Parag Agarwal <agarwal.parag@gmail.com>