Add job for using pbrx to build container images

The pbrx build-images command is directly applicable to any python
project with pbr and bindep. Make a simple job that will run pbrx
to produce images.

Change-Id: Ica28f42bd0acc78a0e960ceef30e5e5045e8b389

.zuul.yaml

@@ -1,3 +1,11 @@
+- job:
+    name: pbrx-build-container-images
+    nodeset: ubuntu-bionic
+    required-projects:
+      - openstack/pbrx
+    pre-run: playbooks/container-images/pre.yaml
+    run: playbooks/container-images/run.yaml
+
 - project:
     check:
       jobs:

playbooks/container-images/pre.yaml

@@ -0,0 +1,11 @@
+- hosts: all
+  roles:
+
+    - install-docker
+
+- hosts: all
+  tasks:
+
+    - name: Install pbrx software
+      command: python3 -m pip install src/git.openstack.org/openstack/pbrx
+      become: yes

playbooks/container-images/run.yaml

@@ -0,0 +1,10 @@
+- hosts: all
+  tasks:
+
+    - name: reset ssh connection to pick up docker group
+      meta: reset_connection
+
+    - name: Build zuul container images
+      command: pbrx --debug build-images
+      args:
+        chdir: src/git.openstack.org/openstack-infra/zuul