MB-11224:  rel-2.5.1.1.xml identical to 2.5.1 release
           override manifests identical to 2.5.1 release, except revision="3.21.17-couchbase" for v8

Change-Id: I67228658b6ab7b8e67aae36fb81904ebb4a61bd5
Reviewed-on: http://review.couchbase.org/37633
Reviewed-by: Chris Hillery <ceej@couchbase.com>
Tested-by: Chris Hillery <ceej@couchbase.com>