Enable test coverage in tox

tox for cover doesn't work well.
This patch fix it.

{{cookiecutter.repo_name}}/tox.ini

@@ -23,7 +23,11 @@ commands = flake8 {posargs}
 commands = {posargs}
 
 [testenv:cover]
-commands = python setup.py test --coverage --testr-args='{posargs}'
+commands =
+  coverage erase
+  coverage run {toxinidir}/manage.py test {{cookiecutter.module_folder}} --settings={{cookiecutter.module_folder}}.test.settings {posargs} --exclude-dir={{cookiecutter.module_folder}}/test/integration_tests {posargs}
+  coverage xml --omit '.tox/cover/*' -o 'cover/coverage.xml'
+  coverage html --omit '.tox/cover/*' -d 'cover/htmlcov'
 
 [testenv:py27dj18]
 basepython = python2.7