Return function to schedule saving sensors.

def _create_scheduler(self, save_sensors):
        """Return function to schedule saving sensors."""
        @asyncio.coroutine
        def schedule_save():
            """Save sensors and schedule a new save."""
            yield from self.loop.run_in_executor(None, save_sensors)
            callback = partial(self.loop.create_task, schedule_save())
            task = self.loop.call_later(10.0, callback)
            self._cancel_save = task.cancel
        return schedule_save