zuul: run standalone job with locally built images

We now want to test the CLI that builds the container images, so we
picked standalone job and will run the same job except that instead of
pulling images from a remote registry, we'll build them locally and use
them for the deployment.

Depends-On: https://review.opendev.org/729824
Depends-On: https://review.opendev.org/729465
Depends-On: https://review.opendev.org/734870
Depends-On: https://review.opendev.org/733388

Change-Id: I4b30c0c2478d401babe3e690bd54b2853201baab

zuul.d/layout.yaml

@@ -22,6 +22,10 @@
             dependencies: *deps_unit_lint
             files:
               - ^tripleoclient/v2/tripleo_container_image.py$
+        - tripleo-ci-centos-8-standalone:
+            dependencies: *deps_unit_lint
+            vars:
+              build_container_images: true
         - tripleo-ci-centos-8-scenario000-multinode-oooq-container-updates:
             dependencies: *deps_unit_lint
         - tripleo-ci-centos-8-scenario001-standalone: