Add more tests of the MockClients

Change-Id: I7b6f394f48c5e83eab5701f10a56e7eb66760cd4
Reviewed-on: http://review.couchbase.org/27911
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>
Tested-by: Trond Norbye <trond.norbye@gmail.com>