Add openstack-python36-jobs-horizon variant

This is similar to the existing openstack-python35-jobs-horizon
template, which is needed for dashboard projects, just with py36
instead.

Change-Id: I492fc3d02066bf79d2556a034fcd55b502cfc9e0
Needed-By: https://review.openstack.org/584890

zuul.d/project-templates.yaml

@@ -515,6 +515,23 @@
       jobs:
         - openstack-tox-py36
 
+- project-template:
+    name: openstack-python36-jobs-horizon
+    description: |
+      The standard openstack-python36-jobs but with horizon added as a
+      required-projects. The dashboard projects currently need this
+      due to how the tox_install.sh zuul-cloner's horizon for them.
+    check:
+      jobs:
+        - openstack-tox-py36:
+            required-projects:
+              - openstack/horizon
+    gate:
+      jobs:
+        - openstack-tox-py36:
+            required-projects:
+              - openstack/horizon
+
 - project-template:
     name: openstack-python36-jobs-neutron
     check: