Starts the mock S3 server on the given port at the given path.

def start(port, root_directory, bucket_depth):
    """Starts the mock S3 server on the given port at the given path."""
    application = S3Application(root_directory, bucket_depth)
    http_server = httpserver.HTTPServer(application)
    http_server.listen(port)
    ioloop.IOLoop.current().start()