Catch the 429 response (throttled by sentry)

When we get throttled by Sentry (which is hard to avoid if we have e.g. a database issue that dumps a stack trace for every request) Raven was writing the entire response body to the log, which in this case is an HTML page. This makes the logs unreadable.

This patch will:
- log a warning on 429 (too many requests)
- avoid dumping the massive HTML page that it returns into the log, by not calling getInputStream().close() in that case.

Thanks