kqueue tests: Simplify the test runner

Just invoke the test program directly instead of trying to convert its
output to TAP format. The test suite is all or nothing; there's no way
to enumerate individual test cases, so there's no advantage in trying to
massage its output, and doing so throws away information that's useful
when diagnosing test failures.

Sponsored by: The FreeBSD Foundation

(cherry picked from commit 68fe988a40ca5dedec426735f52471d9af7bddbd)