Detect shutdown and exit cleanly

[mnlevy1981]

If I run jupyter lab locally from a terminal then jupyter runs while I do whatever I need to do in the web browser. If I finish using the jupyter kernel and select File... Shutdown from the jupyter web menu, then that kills the local jupyter and I can go back to using my terminal.

If I have launched the lab via jupyter-forward, however, the script faithfully reports that the kernel has shutdown

[I 16:06:39.281 LabApp] Shutting down on /api/shutdown request.
[I 16:06:39.285 LabApp] Shutting down 0 kernels
[I 16:06:39.285 LabApp] Shutting down 0 terminals

but I still need to ^C my way out of the script itself. Perhaps we can figure out some reasonable criteria for jupyter-forward to exit cleanly?