CBD-1425:  add property PRODUCT=couchbase-server

use LATEST=http://10.1.2.98/${PRODUCT}/${RELEASE}/${REVISION} to
fetch current.xml from buildbot master latestbuilds

Change-Id: I51885660c334de6f783c6b23f03abeb001d4473f
Reviewed-on: http://review.couchbase.org/40851
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>