Use bionic images for zuul-stream-functional tests

Zuul now requires at least python 3.6 so use the bionic image for the
zuul-stream-functional tests as well.

Change-Id: Iba47cd9733e97fba5b0471fdcfc69588f03f85d9

.zuul.yaml

@@ -2,11 +2,11 @@
     name: zuul-functional-temp-master
     nodes:
       - name: controller
-        label: ubuntu-xenial
+        label: ubuntu-bionic
       - name: node1
-        label: ubuntu-xenial
+        label: ubuntu-bionic
       - name: node2
-        label: ubuntu-xenial
+        label: ubuntu-bionic
     groups:
       - name: node
         nodes:

playbooks/zuul-stream/functional.yaml

@@ -1,9 +1,8 @@
 - hosts: controller
   tasks:
-
     - name: Set python path fact
       set_fact:
-        python_path: "/usr/local/lib/python3.5/dist-packages"
+        python_path: "/usr/local/lib/python3.6/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/python3.5/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/python3.6/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