Add nova/neutron project unit/functional tests job in gate

We do not test the olso policy master code changes with
services unit or functional tests. Tempest job initialize
policy once and run with default rules so it will not be able
to catch all the scenario what unit or functional job does.
They initialize or override policy in parallel and sometime
that help to find the issue like
- https://bugs.launchpad.net/oslo.policy/+bug/1914095

Also this will help us to avoid any new breaking release which
is detected at the time when requirement u-c are updated
Example: https://review.opendev.org/c/openstack/requirements/+/773779

Currently this commit adds only nova & neutron testing but we can add
more service testing later.

Change-Id: Ic54b229a4bf1325adac2cab747bcd19b9f8ecb01

.zuul.yaml

@@ -1,3 +1,39 @@
+- job:
+    name: cross-nova-tox-functional
+    parent: openstack-tox
+    description: |
+      Run cross-project functional tests on nova.
+    vars:
+      zuul_work_dir: src/opendev.org/openstack/nova
+      tox_envlist: functional
+    required-projects:
+      - openstack/nova
+      - openstack/oslo.policy
+
+- job:
+    name: cross-nova-tox-py38
+    parent: openstack-tox
+    description: |
+      Run cross-project unit tests on nova.
+    vars:
+      zuul_work_dir: src/opendev.org/openstack/nova
+      tox_envlist: py38
+    required-projects:
+      - openstack/nova
+      - openstack/oslo.policy
+
+- job:
+    name: cross-neutron-tox-py38
+    parent: openstack-tox
+    description: |
+      Run cross-project unit tests on neutron.
+    vars:
+      zuul_work_dir: src/opendev.org/openstack/neutron
+      tox_envlist: py38
+    required-projects:
+      - openstack/neutron
+      - openstack/oslo.policy
+
 - project:
     templates:
       - check-requirements
@@ -7,3 +43,13 @@
       - periodic-stable-jobs
       - publish-openstack-docs-pti
       - release-notes-jobs-python3
+    check:
+      jobs:
+        - cross-nova-tox-py38
+        - cross-nova-tox-functional
+        - cross-neutron-tox-py38
+    gate:
+      jobs:
+        - cross-nova-tox-py38
+        - cross-nova-tox-functional
+        - cross-neutron-tox-py38