fix em-synchrony test to use mock

Change-Id: Ia55646bea4684abeeffb4fdb71e8abce2b1a6ece
Reviewed-on: http://review.couchbase.org/38106
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>