Add queue lengths to the zuul status page.

Change-Id: Ib147641c6c41aedc3deea30b5b1e3e5f7b68c103
Reviewed-on: https://review.openstack.org/23109
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: James E. Blair <corvus@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins