Arvados

EventClient and PollClient in the Python SDK should be catching exceptions in a couple of places that it currently does not, which results in the event thread crashing and thing that depend on it getting wedged:

• The callback to user code, to avoid crashing the event handler thread
  • When this happens, call thread.interrupt_main() to raise an exception in the main thread, and force it to deal with the error.
• When PollClient makes calls to the API server
  • Use the same style of RetryLoop that one_task_per_input_file uses. It can retry infinitely, but take care that the backoff numbers make sense.
• Test that PollClient retries API failures.