use pytest for end2end tests

Author: asherf

tox.ini

@@ -15,8 +15,9 @@ changedir =
     end2end: {toxinidir}/django_prometheus/tests/end2end
 setenv =
     end2end: PYTHONPATH = {toxinidir}
+    end2end: DJANGO_SETTINGS_MODULE=testapp.settings 
 commands =
-    end2end: coverage run --source=django_prometheus manage.py test
+    end2end: coverage run --source=django_prometheus -m pytest testapp/
     unittests: coverage run --source=django_prometheus setup.py test
     unittests: python setup.py sdist bdist_wheel