CBQE-2478: n1ql stats tests

Change-Id: Ia9298e37343d1d65a2050b53d60b76dd213d1621
Reviewed-on: http://review.couchbase.org/43487
Reviewed-by: Ketaki Gangal <ketakigangal@gmail.com>
Tested-by: buildbot <build@couchbase.com>