CBQE-0 :: fix warm up bug when flow control is set, add sleep

Change-Id: I4a5e7e005c02deba2964e3bbf6336e73cc8abfb2
Reviewed-on: http://review.couchbase.org/38002
Reviewed-by: Parag Agarwal <agarwal.parag@gmail.com>
Tested-by: Parag Agarwal <agarwal.parag@gmail.com>