MB-8582: Move make_key_options/1 into mapreduce_view module

To make the couch_set_views more indexer agnostic all indexers
will need a make_key_options/1 function (the one of the spatial
indexer will be a no-op). Hence it's moved from couch_set_view_utils
to the mapreduce_view module.

Change-Id: I28483912428474af1b7bdf56bcfc647a6b309df6
Reviewed-on: http://review.couchbase.org/27613
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>
Tested-by: buildbot <build@couchbase.com>