unlock ep-engine, use "2.5.0" branch

Change-Id: I2fc8ccb60434d7dd28fd7821d3ac5172cc2d40ab
Reviewed-on: http://review.couchbase.org/31748
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>