Automatically drop models from config.

[adriaanwm]

Instead of manually adding each model used in tests in the tests/init.py file, drop collections from config list.

eg.

class BaseTestCase(TestCase):
    ...

    def tearDown(self):
        self.__teardown_models()

    def __teardown_models(self):
        for model in config.MODELS:
            module = importlib.import_module(
                'app.models.{0}'.format(model)
            )
            try:
                getattr(module, to_camel_case(model)).drop_collection()
            except AttributeError:  # EmbeddedDocuments don't have drop_collection
                pass


def to_camel_case(snake):
    return ''.join([x.title() for x in snake.split('_')])