Delete this VM (including all its files).

def delete(self):
        """
        Delete this VM (including all its files).
        """
        try:
            yield from wait_run_in_executor(shutil.rmtree, self._working_directory)
        except OSError as e:
            log.warn("Could not delete file {}".format(e))

        self.manager.release_dynamips_id(self._project.id, self._dynamips_id)