Use templates for cover and lower-constraints

Use openstack-tox-cover template, this runs the cover job
in the check queue only.

Use openstack-lower-constraints-jobs template.

Remove jobs that are part of the templates.

Change-Id: I21efefc2e85c57d754b272b02de694f5c6a6edfd

.zuul.yaml

@@ -1,17 +1,12 @@
 - project:
     templates:
+      - openstack-cover-jobs
+      - openstack-lower-constraints-jobs
       - openstack-python-jobs
       - openstack-python35-jobs
       - openstack-python36-jobs
       - release-notes-jobs-python3
       - publish-openstack-docs-pti
       - check-requirements
-    check:
-      jobs:
-        - openstack-tox-lower-constraints
-        - openstack-tox-cover:
-            voting: false
     gate:
       queue: kuryr
-      jobs:
-        - openstack-tox-lower-constraints