CBD-767: use the same ddocs for different index phases

Change-Id: Ie8e9b2a48297de0d16f9df26b60c457ce6501c08
Reviewed-on: http://review.couchbase.org/24177
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: Pavel Paulau <pavel.paulau@gmail.com>