Use templates for cover and lower-constraints

Small cleanups:

* Use openstack-tox-cover template, this runs the cover job
  in the check queue only. Remove individual cover jobs.
* Use openstack-lower-constraints-jobs template, remove individual
  jobs.
* Sort list of templates

Change-Id: I75bf468d7e59282377bd78f4d236f07e3c9c596f

zuul.d/project.yaml

@@ -1,24 +1,20 @@
 - project:
     templates:
+      - check-requirements
+      - openstack-cover-jobs
+      - openstack-lower-constraints-jobs
+      - openstack-python-jobs
       - openstack-python35-jobs
       - openstack-python36-jobs
-      - openstack-python-jobs
-      - publish-openstack-docs-pti
-      - check-requirements
-      - release-notes-jobs-python3
       - openstackclient-plugin-jobs
+      - publish-openstack-docs-pti
+      - release-notes-jobs-python3
     check:
       jobs:
         - ironicclient-dsvm-functional
         - ironicclient-tempest-dsvm-src
-        - openstack-tox-lower-constraints
-        - openstack-tox-cover
     gate:
       queue: ironic
       jobs:
         - ironicclient-dsvm-functional
         - ironicclient-tempest-dsvm-src
-        - openstack-tox-lower-constraints
-    post:
-      jobs:
-        - openstack-tox-cover