Issue #533: rescue StandardError only

[ColinDKelley]

Address issue #533 by only rescuing StandardError (the default) rather than Exception.

[ColinDKelley]

@ioquatix can you please review?
This is what you originally recommended: simply rescue StandardError. At the time I argued to rescue more, because Ruby could wind up burying other exceptions. But I'm backing away from that based on

1. Noise that was getting logged as reported here: Don't log SystemExit as an error #532
2. The fact that modern Ruby has report_on_exception = true by default, so exceptions that sneak by will still be logged to (to STDERR I believe, which is good enough in k8s). Also, such exceptions get re-raised if you join the thread later. These seem sufficient to address my concerns.

[ioquatix]

When rescuing StandardError I normally call the variable error rather than exception.

LGTM.

[ColinDKelley]

@ioquatix Re error vs. exception, I decided to leave it exception since all the surrounding methods call it that too. I don't see any harm in being a bit more precise. (All exceptions are errors, but not all errors are exceptions.)