moved django test app settings to the django test app module

... to guarantee the settings get executed before any code in that app. Since
python's unittest.TestLoader does not guarantee in what order it will import
modules while hunting for test cases, the unit tests could fail to even load if
tests.django_test_app.models was loaded before tests.test_django. This failure
was seen on ARM machines, which happened to traverse the module tree in an
inconvenient order.