Add gerrit's zuul/jobs repo
Add gerrit's zuul/jobs repo

So that we can pull in roles defined in gerrit's zuul/jobs, add it
to our zuul. We don't want to pull in job definitions (yet), so leave
it in the empty objects list.

Change-Id: If008c158755220e8c9445b63f32c296843ab48f7

openstack-infra/project-config,openstack-infra/project-config