Build containers for single consumer job

Make standalone job build containers when there is one single
consumer job in layout. Do not run content provider jobs in
this case.

Change-Id: I9c46c38458e7bddb973ddbb747d2d0b8497e032e
(cherry picked from commit 9ea51ac8bc)

.zuul.yaml

@@ -18,6 +18,7 @@
     description: |
       TripleO standalone Job running Cinder specific Tempest tests.
     vars:
+      build_container_images: true
       featureset_override:
         run_tempest: false
         tempest_services: