Print exception traceback to stderr

[rakovskij-stanislav]

karton/karton/core/karton.py

Line 208 in d024443

self.log.exception("Failed to process task - %s", self.current_task.uid)

For now, failed task makes these things:

• prints "Failed to process task - %s", self.current_task.uid to logs
• saves traceback in task body
• sets Crashed status on task

It could be useful also to optionally print the whole traceback in stderr. So I suggest to add this feature via flag karton.print_exception_to_stderr