Replace testing template with individual jobs

Being on an independent release model, rbd-iscsi-client supports
more pythons than are supported by current openstack development,
so adjust the zuul and tox config to reflect this.

Also temporarily makes the pep8 job non-voting so this change
can be merged.  The pep8 job is fixed and restored to voting by
change Ia4d40a85ac15.

Change-Id: I0042e16d19e133546b0384fec5a6aee1701eda28

.zuul.yaml

@@ -1,14 +1,33 @@
 - project:
     templates:
-      - openstack-python3-xena-jobs
+      # NOTE: we don't use the openstack-python3 jobs template here
+      # because being on an independent release model, we support
+      # more than the required pythons
+
       - publish-openstack-docs-pti
       - check-requirements
       - release-notes-jobs-python3
+
     check:
       jobs:
+        - openstack-tox-pep8:
+            # TODO: make voting when pep8 job is fixed
+            voting: false
+        - rbd-iscsi-client-py36
+        - openstack-tox-py38
+        - openstack-tox-py39
         - rbd-iscsi-client-code-coverage:
             voting: false
 
+    gate:
+      jobs:
+        - openstack-tox-pep8:
+            # TODO: make voting when pep8 job is fixed
+            voting: false
+        - rbd-iscsi-client-py36
+        - openstack-tox-py38
+        - openstack-tox-py39
+
 - job:
     name: rbd-iscsi-client-code-coverage
     parent: openstack-tox-cover
@@ -22,3 +41,13 @@
       - ^setup.cfg$
       - ^tools/.*$
       - ^tox.ini$
+
+- job:
+    name: rbd-iscsi-client-py36
+    parent: openstack-tox-py36
+    # NOTE: zuul ignores TOX_CONSTRAINTS_FILE and uses upper constraints
+    # directly from the requirements repo, so we need to tell it to use
+    # the u-c from a branch that still supports py36
+    required-projects:
+      - name: openstack/requirements
+        override-checkout: stable/yoga

setup.cfg

@@ -22,6 +22,7 @@ classifiers =
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
+    Programming Language :: Python :: 3.9
 
 [global]
 setup-hooks =

tox.ini

@@ -32,6 +32,14 @@ allowlist_externals = bash
                       find
 passenv = http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY
 
+[testenv:py36]
+# We have to override the tox default py36 testenv because we need to use
+# upper constraints from the last openstack release that supports python 3.6
+deps =
+    -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/yoga}
+    -r{toxinidir}/test-requirements.txt
+    -r{toxinidir}/requirements.txt
+
 [testenv:pep8]
 commands = flake8 {posargs}