fixes bug 924417 - Improve timeouts on crontabber ftpscraper?

@rhelmer || @twobraids || @AdrianGaudebert r?

The idea here is that every time we do `urllib2.urlopen(url)` we wrap it in a wrapper that sleeps and retries if we get any `URLError` or a HTTP error with a `>= 500` error because almost always, those errors are just temporary.