force returncode of 0 so handlers aren't skipped for failed jobs

Currently, if the return code of a periodic test job is not 0 the handlers are skipped, which might make sense for some PR-jobs.
But for the throughput tests, I want the handler to always run even for failed jobs, as I want to persist the logs for those runs.
This is because the throughput test runs over a lot of events so an encountered failure is important to remember and follow up.

Given that we can't predict all failure cases, the handler might also crash, but the copying of the logs happens early in the handler and is the important part.