zuul: Add nova-tox-functional-centos8-py36 job

The nova-tox-functional-py36 job was replaced with the current py38
version during Victoria by I1d6a2986fcb0435cfabdd104d202b65329909d2b.

However as clearly stated in both the Victoria and Xena runtime
reference documents python 3.6 remains supported through CentOS 8 and
later CentOS 8 stream.

This change reintroduces functional test coverage for py36 using a
CentOS 8 stream based job.

[1] https://governance.openstack.org/tc/reference/runtimes/victoria.html
[2] https://governance.openstack.org/tc/reference/runtimes/xena.html

Change-Id: I6ef77bd92f2595016a99d1953414d3f554f6b2eb

.zuul.yaml

@@ -1,6 +1,34 @@
 # See https://docs.openstack.org/infra/manual/drivers.html#naming-with-zuul-v3
 # for job naming conventions.
 
+- job:
+    name: nova-tox-functional-centos8-py36
+    parent: openstack-tox-functional-py36
+    nodeset: devstack-single-node-centos-8
+    description: |
+      Run tox-based functional tests for the OpenStack Nova project
+      under cPython version 3.6 with Nova specific irrelevant-files list.
+      Uses tox with the ``functional-py36`` environment.
+
+      This job also provides a parent for other projects to run the nova
+      functional tests on their own changes.
+    required-projects:
+      # including nova here makes this job reusable by other projects
+      - openstack/nova
+      - openstack/placement
+    irrelevant-files: &functional-irrelevant-files
+      - ^.*\.rst$
+      - ^api-.*$
+      - ^doc/(source|test)/.*$
+      - ^nova/locale/.*$
+      - ^releasenotes/.*$
+    vars:
+      # explicitly stating the work dir makes this job reusable by other
+      # projects
+      zuul_work_dir: src/opendev.org/openstack/nova
+      bindep_profile: test py36
+    timeout: 3600
+
 - job:
     name: nova-tox-functional-py38
     parent: openstack-tox-functional-py38
@@ -15,12 +43,7 @@
       # including nova here makes this job reusable by other projects
       - openstack/nova
       - openstack/placement
-    irrelevant-files: &functional-irrelevant-files
-      - ^.*\.rst$
-      - ^api-.*$
-      - ^doc/(source|test)/.*$
-      - ^nova/locale/.*$
-      - ^releasenotes/.*$
+    irrelevant-files: *functional-irrelevant-files
     vars:
       # explicitly stating the work dir makes this job reusable by other
       # projects
@@ -507,6 +530,7 @@
         - nova-next
         - nova-tox-validate-backport:
             voting: false
+        - nova-tox-functional-centos8-py36
         - nova-tox-functional-py38
         - nova-tox-functional-py39:
             voting: false
@@ -545,6 +569,7 @@
       jobs:
         - nova-live-migration
         - nova-live-migration-ceph
+        - nova-tox-functional-centos8-py36
         - nova-tox-functional-py38
         - nova-multi-cell
         - nova-next