I added `waitpid()`, but that didn't actually help because we were
`daemon()`izing. Don't daemonize if we're testing so that we can `waitpid()`.
Note I still haven't reproduced this race locally, but I'm pretty sure this will
fix it.
While here, actually check the return value from `waitpid()` just in case
something goes wrong there.
Closes: #1084
Approved by: jlebon