[feature request] Timeout waiting for reboot

[gmacon]

I had a hardware failure this morning, and so my CI job that does the deployment with colmena became stuck. I'd like to be able to set a timeout where, if a machine doesn't come back after a certain amount of time, the deployment is considered to have failed. Would y'all be willing to entertain a PR implementing such a feature? I'm currently thinking this would be a single, global value associated with a --reboot-timeout command line option, but there might be a better design.

[bjornfor]

I'm just a user, but if you look into this, I'd be very happy if you'd fix #166 along the way 😄

[gmacon]

Well, I don't know that fixing #166 would be part of this effort, but this could certainly provide a mitigation. It would convert the infinite hang into a failure. I've been using the workaround (setting timeouts & keepalives in SSH) without issues.