CBQE-2447: n1ql: update system syntax

Change-Id: If1974ae8b4f8701659b4b22adbc97bddcfafde9d
Reviewed-on: http://review.couchbase.org/42568
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>