CBD-1425:  check to see if manifest exists, bail with error message

Change-Id: I08f14cec9d6cace40c561e8f30bdba0b83b565fe
Reviewed-on: http://review.couchbase.org/40626
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>