Updating python testing as per Yoga testing runtime

Yoga testing runtime[1] has been updated to add py39
testing as voting. Unit tests update are
handled by the job template change in openstack-zuul-job

- https://review.opendev.org/c/openstack/openstack-zuul-jobs/+/820286

this commit makes other required changes in zuul.yaml and
update the classifier in setup.cfg file.

[1] https://governance.openstack.org/tc/reference/runtimes/yoga.html

Change-Id: I50c125df4ee03377caf16da5824e2ed492d4b7da

.zuul.yaml

@@ -19,10 +19,9 @@
         - openstack-tox-functional-py36
         - openstack-tox-functional-py37
         - openstack-tox-functional-py38
-        - openstack-tox-functional-py39:
-            voting: false
+        - openstack-tox-functional-py39
         - openstack-tox-pep8
-        - placement-nova-tox-functional-py38
+        - placement-nova-tox-functional-py39
         - placement-nested-perfload:
             voting: false
         - placement-perfload:
@@ -53,8 +52,9 @@
         - openstack-tox-functional-py36
         - openstack-tox-functional-py37
         - openstack-tox-functional-py38
+        - openstack-tox-functional-py39
         - openstack-tox-pep8
-        - placement-nova-tox-functional-py38
+        - placement-nova-tox-functional-py39
         - tempest-integrated-placement:
             irrelevant-files: *gate-irrelevant-files
         - grenade:
@@ -67,14 +67,14 @@
         # we only test the latest version in the periodics as its just a signal
         # that we need to investigate the healt of the master branch in the absence
         # of frequent patches.
-        - openstack-tox-functional-py38
-        - openstack-tox-py38
-        - placement-nova-tox-functional-py38
+        - openstack-tox-functional-py39
+        - openstack-tox-py39
+        - placement-nova-tox-functional-py39
         - tempest-integrated-placement
 
 - job:
-    name: placement-nova-tox-functional-py38
-    parent: nova-tox-functional-py38
+    name: placement-nova-tox-functional-py39
+    parent: nova-tox-functional-py39
     description: |
         Run the nova functional tests to confirm that we aren't breaking
         the PlacementFixture.

setup.cfg

@@ -26,6 +26,7 @@ classifier =
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
+    Programming Language :: Python :: 3.9
 
 [files]
 packages =

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 minversion = 3.1.1
-envlist = py38,functional-py38,pep8
+envlist = py39,functional-py39,pep8
 skipsdist = True
 # Automatic envs (pyXX) will use the python version appropriate to that
 # env and ignore basepython inherited from [testenv]. That's what we