Set the ep-engine 2.5.1 manifest to 2.5.0 branch

Change-Id: Iaeda396ec5550c5818f646d6051c210f5ed21e3f
Reviewed-on: http://review.couchbase.org/33760
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>