Preparation for Django 3.2 support

This commit adds a non-voting unit test job with Django 3.2.

Jobs with Django 3.0 and 3.1 are dropped now.
They were introduced before Django 3.2 was released.
Django 3.0 reached EOL and Django 3.1 will reach EOL this December.
Django 3.2 is an LTS version so testing with Django 3.2 is enough.

Change-Id: Ic6ba0ea281b287b7f4762f92e2e81a6fd654da8f

.zuul.d/django-jobs.yaml

@@ -22,16 +22,10 @@
       - name: openstack/horizon
 
 - job:
-    name: horizon-tox-python3-django30
+    name: horizon-tox-python3-django32
     parent: horizon-tox-python3-django
     vars:
-      django_version: '>=3.0,<3.1'
-
-- job:
-    name: horizon-tox-python3-django31
-    parent: horizon-tox-python3-django
-    vars:
-      django_version: '>=3.1,<3.2'
+      django_version: '>=3.2,<3.3'
 
 - project-template:
     name: horizon-non-primary-django-jobs
@@ -45,13 +39,10 @@
         # to keep this project template as it is used in horizon plugins.
         # NOTE: We keep it as a template even though it is not used now.
         - openstack-tox-py38
-        - horizon-tox-python3-django30:
-            voting: false
-        - horizon-tox-python3-django31:
+        - horizon-tox-python3-django32:
             voting: false
     gate:
       jobs:
         - openstack-tox-py38
         # Skip these until the django3.x jobs become voting.
-        # - horizon-tox-python3-django30
-        # - horizon-tox-python3-django31
+        # - horizon-tox-python3-django32

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 minversion = 3.1
-envlist = pep8,py36,py38,releasenotes,npm,py3-dj{30,31}
+envlist = pep8,py36,py38,releasenotes,npm,py3-dj32
 skipsdist = True
 # Automatic envs (pyXX) will only use the python version appropriate to that
 # env and ignore basepython inherited from [testenv] if we set
@@ -15,6 +15,11 @@ setenv =
   PYTHONDONTWRITEBYTECODE = 1
   PYTHONWARNINGS = once,ignore::PendingDeprecationWarning
   py{3,36,37}:PYTHONWARNINGS = once,ignore::PendingDeprecationWarning,ignore::ImportWarning:backports
+  # DeprecationWarning is disabled in dj32 tox env as Django 3.2
+  # deprecated Django 2.2 features. This workaround is just to reduce
+  # the number of warnings due to this change.
+  # It should be dropped when we drop Django 2.2 support.
+  dj32: PYTHONWARNINGS = once,ignore::PendingDeprecationWarning,ignore::DeprecationWarning
 
 whitelist_externals =
   bash
@@ -26,8 +31,7 @@ deps =
   # Unit test for a local hacking rule requires hacking.
   hacking>=3.0.1,<3.1.0 # Apache-2.0
 commands =
-  dj30: pip install django>=3.0,<3.1
-  dj31: pip install django>=3.1,<3.2
+  dj32: pip install django>=3.2,<3.3
   find . -type f -name "*.pyc" -delete
   bash {toxinidir}/tools/unit_tests.sh {toxinidir} {posargs}