Don't do copy constructors for mock commands

Change-Id: I0e149f8c1ac660d6fedc8db3d64176de360b1874
Reviewed-on: http://review.couchbase.org/28117
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>