import zuul job settings from project-config

This is a mechanically generated patch to complete step 1 of moving
the zuul job settings out of project-config and into each project
repository.

Because there will be a separate patch on each branch, the branch
specifiers for branch-specific jobs have been removed.

Because this patch is generated by a script, there may be some
cosmetic changes to the layout of the YAML file(s) as the contents are
normalized.

See the python3-first goal document for details:
https://governance.openstack.org/tc/goals/stein/python3-first.html

Change-Id: If180d34ebe1ee8a7ff5dcd005c3709a76beeade1
Story: #2002586
Task: #24312

.zuul.yaml

@@ -1,7 +1,16 @@
 - project:
+    templates:
+      - openstack-python-jobs-horizon
+      - check-requirements
     check:
       jobs:
         - openstack-tox-lower-constraints
+        - openstack-tox-py35:
+            required-projects:
+              - openstack/horizon
     gate:
       jobs:
         - openstack-tox-lower-constraints
+        - openstack-tox-py35:
+            required-projects:
+              - openstack/horizon