Fixup copying in MockResponse

This copies pointers and causes accidental double-frees

Change-Id: If35ef6e62fae56a23eeeb8cf352e09765f2f791b
Reviewed-on: http://review.couchbase.org/32633
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>