queue sub-commands need to know how to catch URLError and exit "handled error" QueueEngine defines handled_error_code which is used by sub-commands to indicate that the the command failed, but that the subcommand handled it, or that the error was temporary. subcommands need to know how to handle URLErrors from StatusBot and report them as being temporary to the parent queue. https://bugs.webkit.org/show_bug.cgi?id=32940#c10