Jenkins slave reboot doesn't work if build doesn't complete

We want to automatically reboot Jenkins slaves at the end of each test run (or somehow otherwise ensure a clean state between runs).

The current mechanism we have is simply to run a 'reboot' command (or shutdown /r on Windows) after test.pl has completed (saving the exit code of test.pl to return later).

This completely fails to work if the job is interrupted for some reason, e.g. the build is canceled, interrupted due to network issues, etc.

At the very least, we really need it to work if the job is canceled.

It would be nice if it also works in rarer error cases, such as when the Jenkins slave itself has some problem (e.g. an outdated slave.jar).