CCBC-283 Apply key prefix in cbc-pillowfight

Change-Id: I0309fbd548ac3f94c4f9a750c63d547770c4ef4a
Reviewed-on: http://review.couchbase.org/29626
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>