Add .zuul.yaml and .stestr.conf

Define jobs to run on the repo. lower-constraints is omitted for now
because there is no tox env. It can be added in a follow up patch.

.stestr.conf was missed in the stestr migration patch, which causes all of
the unit tests to fail.

Change-Id: Ie944875fe0ff8725416d50a7ff737559fe9d1f3a

.stestr.conf

@@ -0,0 +1,3 @@
+[DEFAULT]
+test_path=./oslo_upgradecheck
+top_dir=./

.zuul.yaml

@@ -0,0 +1,10 @@
+- project:
+    templates:
+      - publish-openstack-docs-pti
+      - openstack-python-jobs
+      - openstack-python35-jobs
+      - check-requirements
+      - lib-forward-testing
+      - lib-forward-testing-python3
+      - periodic-stable-jobs
+      - openstack-python36-jobs