can we shutdown a scheduler with a wait time?

I hope we can call the shutdown method like this:

```
# wait 3s to shutdown the job. Replace wait=False with wait=3s.
scheduler.shutdown(wait=3)
```

Because sometime the jobs can hanged because of bad networking.
I wan't to wait the jobs done, but sometime it can be hanging for a day.

Is there any way to do it? If not, how about add the feature in the next version?