Set rel-2.5.0.xml ep-engine revision 2.5.0 branch

At time of code freeze for 2.5.0 this branch may be
set to point to a specific revision id

Change-Id: I915d8de69542dcdc3116d3effcfe7433da6dca3f
Reviewed-on: http://review.couchbase.org/29701
Reviewed-by: Sundararaman Sridharan <sundar.sridharan@gmail.com>
Tested-by: Sundararaman Sridharan <sundar.sridharan@gmail.com>