runtests: display the test status if tests appear hung

runtests: display the test status if tests appear hung

It sometimes happens that a test hangs during a test run and never
returns. The test harness will wait indefinitely for the results and on
CI servers the CI job will eventually be killed after an hour or two.
At the end of a test run, if results haven't come in within a couple of
minutes, display the status of all test runners and what tests they're
running to help in debugging the problem.

This feature is really only kick in with parallel testing enabled, which
is fine because without parallel testing it's usually easy to tell what
test has hung.

Closes #11980