Run releasenotes jobs only on liberty and newer

Do not run releasenotes jobs on juno and kilo,
just on liberty, master and future stable branches.

Make it non-voting for now until reno works fine - and thus
remove the job from the gate. This gives projects
also the change to get all infrastructure in place.

Change-Id: Icf6d68ed76a23a680af169fb758fbfd3af6dc168

zuul/layout.yaml

@@ -466,8 +466,6 @@ project-templates:
   - name: release-notes-jobs
     check:
       - 'gate-{name}-tox-releasenotes'
-    gate:
-      - 'gate-{name}-tox-releasenotes'
 
   - name: openstack-server-release-jobs-constraints
     pre-release:
@@ -2066,6 +2064,10 @@ jobs:
   - name: gate-tempest-dsvm-neutron-full-ssh
     voting: false
 
+  - name: ^gate-.*-tox-releasenotes$
+    branch: ^(?!stable/(?:juno|kilo)).*$
+    voting: false
+
   # Constraints Jobs
   - name: ^gate-.*-constraints$
     branch: ^(?!stable/(?:juno|kilo)).*$