Add a script to start the mock server

Change-Id: I458fae3123c61b22c6270cae1f5a7ad2acce96ba
Reviewed-on: http://review.couchbase.org/24216
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>