Copy S3 data to a local file.

def download(self, remote_url, local_path, buffer_size=8 * 1024):
        """Copy S3 data to a local file."""
        bucket, key = _parse_url(remote_url)

        response_file = self.call("GetObject", bucket=bucket, key=key)['Body']
        with open(local_path, 'wb') as fp:
            buf = response_file.read(buffer_size)
            while buf:
                fp.write(buf)
                buf = response_file.read(buffer_size)