[Runner] Attach the coredump when a test crashed
When a test crashes on a particular machine in CI, it can be quite difficult to figure out why. By attaching the coredump to the results, we could improve the debug-ability of crashes.
That being said, crashdumps could be quite big, especially if the test allocated a lot of memory, so we need to have some thresholds in place to prevent filling the disk with it.
This depends on #21.