change branch in ep_engine project to toy

Change-Id: I3408caed6220a21c2dfad47a0a12772bfe195bdf
Reviewed-on: http://review.couchbase.org/25252
Reviewed-by: Junyi Xie <junyi.couchbase@gmail.com>
Tested-by: Junyi Xie <junyi.couchbase@gmail.com>