Add kvs sorting step in initial index builder

Change-Id: I7e79d7cd13fb53cb17db4f5fad83f6c1d5963aa0
Reviewed-on: http://review.couchbase.org/32546
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>