Unlike in the correctness tests, the most common cause of non-zero
return seems to be the user interrupting, so killing the run seems
like the friendly thing to do.
This is not near as fancy as as the unit tests, on the theory that
the code should typically be crashing when performance tuning.
Nonetheless, there is plenty of room for improvement. Several more of
the pieces of the test infrastructure (e.g. the option parsing) could
be factored out into test/test-lib-common.sh
