Use the common cover job instead of a custom one

openstack-tox-cover should exectue at least the same steps,
and it also collects the report generated by the of the cover tox
environment which is not saved right now.

Change-Id: I17bae4a75261c065ce2d17fcca3a0282082589f0

.zuul.yaml

@@ -1,7 +1,7 @@
 - project:
     check:
       jobs:
-        - python-tempestconf-tox-cover
+        - openstack-tox-cover
         - python-tempestconf-tempest-devstack-admin
         - python-tempestconf-tempest-devstack-demo
         - python-tempestconf-tempest-packstack-admin
@@ -15,17 +15,6 @@
         - python-tempestconf-tempest-packstack-demo
         - tripleo-ci-centos-7-scenario002-multinode-oooq-container
 
-- job:
-    name: python-tempestconf-tox-cover
-    parent: openstack-tox
-    description: Run tox code coverage tests.
-    irrelevant-files:
-      - ^.*\.rst$
-      - ^doc/.*$
-      - ^releasenotes/.*$
-    vars:
-      tox_envlist: cover
-
 - job:
     name: python-tempestconf-devstack-base
     parent: devstack