CBQE-0: fix persistence test

Change-Id: I3447b958a7995cde9b0d7be84488152b2d56f26e
Reviewed-on: http://review.couchbase.org/37529
Reviewed-by: Parag Agarwal <agarwal.parag@gmail.com>
Tested-by: Parag Agarwal <agarwal.parag@gmail.com>