Explicitly set the log level to warning.

I use Rocket for a couple of lightweight Python web applications, and really like its simplicity (and name!) when combined with bottle. However, one frustrating item is that if I set my application's basic log level to debug, it propagates down into Rocket and I get tons of unnecessary log messages.

I suggest the included change, which explicitly sets the Rocket log level. If a user wants to override this setting later, it's quite easy to do external to Rocket:

    logging.getLogger('Rocket').setLevel(logging.DEBUG)