Close all the running tasks watching for a container timeout. All references to
            containers are removed: any attempt to was_killed after a call to clean() will return None.

async def clean(self):
        """ Close all the running tasks watching for a container timeout. All references to
            containers are removed: any attempt to was_killed after a call to clean() will return None.
        """
        for x in self._running_asyncio_tasks:
            x.cancel()
        self._container_had_error = set()
        self._watching = set()
        self._running_asyncio_tasks = set()