arrow

ARROW-12376: [Dev] Log traceback for unexpected exceptions in archery trigger-bot

Some earlier attempts at invoking Crossbow failed and the reason wasn't clear. This logs full tracebacks for unexpected exceptions to make it easier to tell what happened.

Example where we ran into a mysterious error: https://github.com/apache/arrow/pull/9941#issuecomment-819363464

Closes #10037 from lidavidm/arrow-12376

Authored-by: David Li <li.davidm96@gmail.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>