Prefix circuit breaker log messages with class name
Logging cleanup

- Override `to_s` with only the relevant information (prevents the
  entire `Rails.cache` object from being dumped every log event,
  massively bloating the logs)
- Rewrite the one log message in this class to be a bit clearer
Merge pull request #3 from envato/clean-up-circuit-breaker-logging

Clean up circuit breaker logging