Update coverage environment and use template for cover

After switch to using stestr, testrepository is unnecessary
and it is removed in patch[1]. After patch[1] got merged
tox -e cover returns "error: option --coverage not recognized".

In this patch fixed coverage environment to default stestr setup.
Also used openstack-tox-cover template, this runs the cover job
in the check queue only.

[1]: https://review.openstack.org/#/c/581686/
Closes-Bug: #1809230

Change-Id: I77a295a64e2c4d128a6772e400c0968f40d11c1d

.zuul.yaml

@@ -1,6 +1,7 @@
 - project:
     templates:
       - check-requirements
+      - openstack-cover-jobs
       - openstack-python-jobs
       - openstack-python35-jobs-nonvoting
       - release-notes-jobs-python3

tox.ini

@@ -52,8 +52,14 @@ commands = {posargs}
 
 [testenv:cover]
 basepython = python3
-commands = python setup.py test --coverage --testr-args='{posargs}'
-           coverage report
+setenv =
+    VIRTUAL_ENV={envdir}
+    PYTHON=coverage run --source masakari --parallel-mode
+commands =
+    stestr run {posargs}
+    coverage combine
+    coverage html -d cover
+    coverage xml -o cover/coverage.xml
 
 [testenv:docs]
 basepython = python3