Sometimes Ruby driver builds get stuck in a test, thus tying up one or more (currently 2) out of our 5 build slots for 30 minutes. This is bad. Additionally we don't have a way of knowing which test is stuck with the fuubar formatter.

A solution addressing both problems is a per-test wall clock time cap, set to e.g. 30 seconds. This can be done with timeout-interrupt which recently landed for one of the PRs. The timeout would 1) abort stuck tests and 2) say which tests get stuck.

Today's stuck tests are MRI, one head and one not head.