Don't make mock tests conditional on --build-plugins

Change-Id: I94f5b21f48de037e8a0aad50dfef6869cb0d620a
Reviewed-on: http://review.couchbase.org/29763
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>