run-selenium: run selenium on a node

This runs selenium from a container on a node, and exposes port 4444
so you can issue commands to it.  This is used in the follow-on
I56cda99790d3c172e10b664e57abeca10efc5566 to take some screenshots of
gerrit.

Change-Id: Idcbcd9a8f33bd86b5f3e546dd563792212e0751b

playbooks/zuul/run-base.yaml

@@ -41,7 +41,11 @@
         bastion_ipv4: "{{ nodepool['public_ipv4'] }}"
         bastion_ipv6: "{{ nodepool['public_ipv6'] }}"
         bastion_public_key: "{{ lookup('file', zuul.executor.work_root + '/' + zuul.build + '_id_rsa.pub') }}"
-        iptables_test_public_tcp_ports: [19885]
+        iptables_test_public_tcp_ports:
+          # Zuul web console
+          - 19885
+          # selenium
+          - 4444
       template:
         src: "templates/{{ item }}.j2"
         dest: "/etc/ansible/hosts/{{ item }}"
@@ -107,6 +111,19 @@
         content: "{{ testinfra_extra_data | default('') | to_nice_yaml(indent=2) }}"
         dest: '/home/zuul/testinfra_extra_data_fixture.yaml'
 
+    - name: Make screenshots directory
+      file:
+        path: '/var/log/screenshots'
+        state: directory
+
+    - name: Return screenshots artifact
+      zuul_return:
+        data:
+          zuul:
+            artifacts:
+              - name: Screenshots
+                url: "bridge.openstack.org/screenshots"
+
     - name: Run and collect testinfra
       block:
         - name: Run testinfra to validate configuration