Migrate functional tests jobs to Ubuntu Focal

As per victoria cycle testing runtime and community goal[1]
we need to migrate upstream CI/CD to Ubuntu Focal(20.04).

This commit migrates:
- openstack-tox-functional & openstack-tox-functional-with-sudo to
ubuntu focal for victoria onwards and bionic from stable/stein till
stable/ussuri and xenial till stable/rocky on xenial.

- openstack-tox-functional-py37 and openstack-tox-functional-py38
to ubuntu focal for victoria onwards and bionic till stable/ussuri

- openstack-tox-py36 will keep running on Ubuntu Bionic as Ubuntu Focal
does not have python 3.6

[1] https://governance.openstack.org/tc/goals/selected/victoria/migrate-ci-cd-jobs-to-ubuntu-focal.html

Change-Id: Ib98d7456529eeeaa10091f17610a646e28ff6f13

zuul.d/jobs.yaml

@@ -357,6 +357,42 @@
 
       Uses tox with the ``functional`` environment.
     irrelevant-files: *common-irrelevant-files
+    branches: ^(?!stable/(ocata|pike|queens|rocky|stein|train|ussuri)).*$
+    vars:
+      tox_envlist: functional
+
+- job:
+    name: openstack-tox-functional
+    parent: openstack-tox
+    description: |
+      Run tox-based (bionic) functional tests for an OpenStack Python project.
+
+      Uses tox with the ``functional`` environment.
+      This job runs on bionic for stable/stein, train, and ussuri.
+    irrelevant-files: *common-irrelevant-files
+    nodeset: ubuntu-bionic
+    branches:
+      - stable/stein
+      - stable/train
+      - stable/ussuri
+    vars:
+      tox_envlist: functional
+
+- job:
+    name: openstack-tox-functional
+    parent: openstack-tox
+    description: |
+      Run tox-based (xenial) functional tests for an OpenStack Python project.
+
+      Uses tox with the ``functional`` environment.
+      This job runs on xenial for stable/rocky.
+    irrelevant-files: *common-irrelevant-files
+    nodeset: ubuntu-xenial
+    branches:
+      - stable/ocata
+      - stable/pike
+      - stable/queens
+      - stable/rocky
     vars:
       tox_envlist: functional
 
@@ -369,6 +405,44 @@
       Uses tox with the ``functional`` environment.
       Sudo access is not revoked.
     irrelevant-files: *common-irrelevant-files
+    branches: ^(?!stable/(ocata|pike|queens|rocky|stein|train|ussuri)).*$
+    vars:
+      tox_envlist: functional
+
+- job:
+    name: openstack-tox-functional-with-sudo
+    parent: openstack-tox-with-sudo
+    description: |
+      Run tox-based (bionic) functional tests for an OpenStack Python project.
+
+      Uses tox with the ``functional`` environment.
+      Sudo access is not revoked.
+      This job runs on bionic for stable/stein, train, and ussuri.
+    irrelevant-files: *common-irrelevant-files
+    nodeset: ubuntu-bionic
+    branches:
+      - stable/stein
+      - stable/train
+      - stable/ussuri
+    vars:
+      tox_envlist: functional
+
+- job:
+    name: openstack-tox-functional-with-sudo
+    parent: openstack-tox-with-sudo
+    description: |
+      Run tox-based (xenial) functional tests for an OpenStack Python project.
+
+      Uses tox with the ``functional`` environment.
+      Sudo access is not revoked.
+      This job runs on xenial till stable/rocky.
+    irrelevant-files: *common-irrelevant-files
+    nodeset: ubuntu-xenial
+    branches:
+      - stable/ocata
+      - stable/pike
+      - stable/queens
+      - stable/rocky
     vars:
       tox_envlist: functional
 
@@ -415,13 +489,33 @@
 - job:
     name: openstack-tox-functional-py38
     parent: openstack-tox
-    nodeset: ubuntu-bionic
+    nodeset: ubuntu-focal
     description: |
       Run tox-based functional tests for an OpenStack Python project
       under cPython version 3.8.
 
       Uses tox with the ``functional-py38`` environment.
     irrelevant-files: *common-irrelevant-files
+    branches: ^(?!stable/(train|ussuri)).*$
+    vars:
+      tox_envlist: functional-py38
+      bindep_profile: test py38
+      python_version: 3.8
+
+- job:
+    name: openstack-tox-functional-py38
+    parent: openstack-tox
+    nodeset: ubuntu-bionic
+    description: |
+      Run tox-based (bionic) functional tests for an OpenStack Python project
+      under cPython version 3.8.
+
+      Uses tox with the ``functional-py38`` environment.
+      This job runs on bionic for stable/train and ussuri.
+    irrelevant-files: *common-irrelevant-files
+    branches:
+      - stable/train
+      - stable/ussuri
     vars:
       tox_envlist: functional-py38
       bindep_profile: test py38