MB-8582: Make more parts indexer agnostic

There were still parts that were specific to the mapreduce_view
indexer. Those are now more generic.

Change-Id: I017eb414f938353f3df3f38a95549b67c80a8630
Reviewed-on: http://review.couchbase.org/27541
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>