test runner - per-test timeout mechanism

[granders]

The test runner should have some ad-hoc mechanism for guessing that a test is in an infinite loop, and terminating the test if has run too long

[ewencp]

Additionally, @gwenshap suggests and I agree it's a good idea:

If individual tests announce timeouts, we can add it to the output
"this test will finish in 600 seconds or timeout", for anxious
developers.

[edenhill]

+1