Add Python 3.6 unit test jobs

To meet the python 3 first community goal[0] this patch adds the
python 3.6 jobs template to octavia-dashboard.

[0] https://governance.openstack.org/tc/goals/stein/python3-first.html

Change-Id: I48730db4c1be14029a1f452cce1b93f817610dd8

zuul.d/projects.yaml

@@ -3,6 +3,7 @@
       - check-requirements
       - openstack-python-jobs-horizon
       - openstack-python35-jobs-horizon
+      - openstack-python36-jobs-horizon
       - publish-openstack-docs-pti
       - release-notes-jobs-python3
     check: