CBD-1246:  2.5.1 manifests are copies of 2.5.0

Change SHA revisions to branch specs to advance.

Change-Id: Ieb774a4715bb627b775b4b8d66cca6f0892a714f
Reviewed-on: http://review.couchbase.org/33456
Reviewed-by: Philip Labee <philip@couchbase.com>
Reviewed-by: Chris Hillery <ceej@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>