MB-100: added write test

Change-Id: I70c0db7e0f719d1d0a923624e2a79c4069f8e7a1
Reviewed-on: http://review.couchbase.org/27674
Reviewed-by: Ronnie Sun <ronnie@couchbase.com>
Tested-by: Ronnie Sun <ronnie@couchbase.com>