Initializes the datastore stub using nosegae config magic

def _init_datastore_v3_stub(self, **stub_kwargs):
        """Initializes the datastore stub using nosegae config magic"""
        task_args = dict(datastore_file=self._data_path)
        task_args.update(stub_kwargs)
        self.testbed.init_datastore_v3_stub(**task_args)