Update coverage environment

Fix coverage environment to default stestr setup.
Update timeout for tox-cover.

Change-Id: I8f7b19743aa3d4b51316c9941bb751ff622fb354

.zuul.yaml

@@ -10,6 +10,8 @@
     name: openstack-infra/storyboard
     check:
       jobs:
+        - tox-cover:
+            timeout: 6000
         - storyboard-tox-sqlite
         - tox-pep8
         - tox-py27:

tox.ini

@@ -43,7 +43,14 @@ commands =
 
 [testenv:cover]
 basepython = python3
-commands = python setup.py testr --coverage --testr-args='{posargs}'
+setenv =
+    VIRTUAL_ENV={envdir}
+    PYTHON=coverage run --source storyboard --parallel-mode
+commands =
+    stestr run {posargs}
+    coverage combine
+    coverage html -d cover
+    coverage xml -o cover/coverage.xml
 
 [flake8]
 # E125 and E128 are ignored on purpose, they are invalid pep8