CBD-1425:  fetch-manifest to output expected build/build/current.xml

Change-Id: Ic0c8edfc29088aaea8a7ecb7649b84324d6fdde5
Reviewed-on: http://review.couchbase.org/40599
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>