Bump test nodes up to Focal

We were running on Bionic because Zuul's inclusion of a pinned Gear
conflicted with TLS policy on Focal. With Gear gone we can bump up to
Focal safely now.

Followup changes can bump testing platforms ahead to 3.9 or newer as
well.

Change-Id: I4cfef79ebc97753994edaf36a1deca0d3b37ad17

.zuul.yaml

@@ -1,12 +1,16 @@
 - nodeset:
     name: zuul-functional-temp-master
     nodes:
+      # python_path in playbooks/zuul-stream/functional.yaml and
+      # callback_plugins in playbooks/zuul-stream/templates/ansible.cfg.j2
+      # need their python versions updated when these labels change to
+      # a platform that uses a different python version.
       - name: controller
-        label: ubuntu-bionic
+        label: ubuntu-focal
       - name: node1
-        label: ubuntu-bionic
+        label: ubuntu-focal
       - name: node2
-        label: ubuntu-bionic
+        label: ubuntu-focal
     groups:
       - name: node
         nodes:
@@ -48,7 +52,7 @@
     description: |
       Zuul unit tests with ZooKeeper running
     parent: tox
-    nodeset: ubuntu-bionic
+    nodeset: ubuntu-focal
     pre-run: playbooks/zuul-tox/pre.yaml
     post-run: playbooks/zuul-tox/post-system-logs.yaml
     vars:
@@ -91,7 +95,6 @@
     vars:
       zuul_work_dir: "{{ zuul.projects['opendev.org/zuul/zuul'].src_dir }}"
       tox_envlist: zuul_client
-    nodeset: ubuntu-bionic
 
 - job:
     name: zuul-tox-py36
@@ -101,6 +104,7 @@
     vars:
       tox_envlist: py36
       python_version: 3.6
+    nodeset: ubuntu-bionic
 
 - job:
     name: zuul-tox-py38

playbooks/zuul-stream/functional.yaml

@@ -2,7 +2,10 @@
   tasks:
     - name: Set python path fact
       set_fact:
-        python_path: "/usr/local/lib/python3.6/dist-packages"
+        # This value is used by Ansible to find the zuul.ansible code
+        # that Zuul's ansible plugins consume. It must be updated when
+        # the python version of the platform is changed.
+        python_path: "/usr/local/lib/python3.8/dist-packages"
 
     - name: Run ansible that should succeed
       command: >

playbooks/zuul-stream/templates/ansible.cfg.j2

@@ -4,7 +4,7 @@ gathering = smart
 gather_subset = !all
 lookup_plugins = {{ ansible_user_dir }}/src/opendev.org/zuul/zuul/zuul/ansible/{{ zuul_ansible_version }}/lookup
 action_plugins = {{ ansible_user_dir }}/src/opendev.org/zuul/zuul/zuul/ansible/{{ zuul_ansible_version }}/actiongeneral:{{ ansible_user_dir }}/src/opendev.org/zuul/zuul/zuul/ansible/{{ zuul_ansible_version }}/action
-callback_plugins = {{ ansible_user_dir }}/src/opendev.org/zuul/zuul/zuul/ansible/{{ zuul_ansible_version }}/callback:/usr/lib/zuul/ansible/{{ zuul_ansible_version }}/lib/python3.6/site-packages/ara/plugins/callbacks
+callback_plugins = {{ ansible_user_dir }}/src/opendev.org/zuul/zuul/zuul/ansible/{{ zuul_ansible_version }}/callback:/usr/lib/zuul/ansible/{{ zuul_ansible_version }}/lib/python3.8/site-packages/ara/plugins/callbacks
 stdout_callback = zuul_stream
 library = {{ ansible_user_dir }}/src/opendev.org/zuul/zuul/zuul/ansible/{{ zuul_ansible_version }}/library
 retry_files_enabled = False