malva: Re-enable Runtime#addShutdownHook test
malva: Re-enable Runtime#addShutdownHook test

It was disabled in commit b1bb3f6bd57d34785fca21f6e9fb9bb69927ee13.
The occasional failure happened because the thread, having nothing to do,
finished before it was expected to be alive.

jatovm/malva,jatovm/malva