CBQE-1531: fix DESC sort order

Change-Id: I2d08ecc1063a8cd7788c85433e095ccb968ccc17
Reviewed-on: http://review.couchbase.org/29447
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>