Enable 2-node gating for Kolla

This adds an experimental job for Kolla to take advantage of n-node
gating.

Change-Id: I9e326fcf0efbf530099bb6a58c59fa0151a0e2e4
Depends-On: I3e05e2d5c739794ae6ff0cc375dc6226f81bb542

jenkins/jobs/projects.yaml

@@ -2255,6 +2255,12 @@
           node: 'devstack-trusty'
           pipeline: gate
           type: source
+      - '{pipeline}-kolla-{action}-images-{distro}-{type}':
+          action: deploy-multinode
+          distro: ubuntu
+          node: 'devstack-trusty-2-node'
+          pipeline: experimental
+          type: source
 
 - project:
     name: kolla-mesos

zuul/layout.yaml

@@ -5656,6 +5656,8 @@ projects:
       - gate-kolla-bashate
       - gate-kolla-pep8
       - gate-kolla-tox-validate-contents
+    experimental:
+      - experimental-kolla-deploy-multinode-images-ubuntu-source
 
   - name: openstack/kolla-mesos
     template: