Start an application
        Args:
            - bundle_id: (string) apk bundle ID

        Returns:
            WDA session object

def start_app(self, bundle_id):
        """Start an application
        Args:
            - bundle_id: (string) apk bundle ID

        Returns:
            WDA session object
        """
        # if self._session is not None:
        #     self.stop_app()
        self._bundle_id = bundle_id
        self._session = self._wda.session(bundle_id)
        return self._session