Create new container build jobs for stein

Define branchful jobs for stein with both docker/buildah.

docker cli:
  - tripleo-build-containers-centos-7
  - tripleo-build-containers-centos-7-stein (NEW*)
  - tripleo-build-containers-centos-7-rocky

buildah cli:
  - tripleo-build-containers-centos-7-buildah
  - tripleo-build-containers-centos-7-buildah-stein (NEW*)

Both Docker and Buildah jobs are voting and gating, however,
buildah ones are not stable for pushing to registry, see
Bug #1824388. None of these jobs push to registry in check/gate.

Will keep duplicate jobs for docker/buildah cli until we
completely switch to buildah.

Related-Bug: #1824388
Story: https://tree.taiga.io/project/tripleo-ci-board/us/815

Change-Id: I20d1546d18f44c8c2da9614cbbd5c15b7d8f88d1

zuul.d/build-containers.yaml

@@ -7,35 +7,51 @@
     check:
       jobs:
         - tripleo-build-containers-centos-7
+        - tripleo-build-containers-centos-7-stein
         - tripleo-build-containers-centos-7-rocky
         - tripleo-build-containers-centos-7-buildah
+        - tripleo-build-containers-centos-7-buildah-stein
     gate:
       queue: tripleo
       jobs:
         - tripleo-build-containers-centos-7
+        - tripleo-build-containers-centos-7-stein
         - tripleo-build-containers-centos-7-rocky
         - tripleo-build-containers-centos-7-buildah
+        - tripleo-build-containers-centos-7-buildah-stein
 
 - job:
     name: tripleo-build-containers-centos-7
     parent: tripleo-build-containers-base-with-files
     nodeset: single-centos-7-node
+    branches: ^(?!stable/(pike|queens|rocky)).*$
     voting: true
 
+- job:
+    name: tripleo-build-containers-centos-7-stein
+    parent: tripleo-build-containers-centos-7
+    override-checkout: stable/stein
+    vars:
+      branch_override: stable/stein
+
 - job:
     name: tripleo-build-containers-centos-7-rocky
-    parent: tripleo-build-containers-base-with-files
-    nodeset: single-centos-7-node
+    parent: tripleo-build-containers-centos-7
     override-checkout: stable/rocky
-    voting: true
     vars:
       branch_override: stable/rocky
 
 - job:
     name: tripleo-build-containers-centos-7-buildah
-    parent: tripleo-build-containers-base-with-files
-    voting: true
-    nodeset: single-centos-7-node
-    branches: ^(?!stable/(pike|queens|rocky)).*$
+    description: |
+      container build job (buildah cli/backend)
+    parent: tripleo-build-containers-centos-7
     vars:
       use_buildah: true
+
+- job:
+    name: tripleo-build-containers-centos-7-buildah-stein
+    parent: tripleo-build-containers-centos-7-buildah
+    override-checkout: stable/stein
+    vars:
+      branch_override: stable/stein