Return a reasonable hostname for a replset membership event to mention.

def hostname_for_event(self, clean_server_name):
        """Return a reasonable hostname for a replset membership event to mention."""
        uri = urlsplit(clean_server_name)
        if '@' in uri.netloc:
            hostname = uri.netloc.split('@')[1].split(':')[0]
        else:
            hostname = uri.netloc.split(':')[0]
        if hostname == 'localhost':
            hostname = self.hostname
        return hostname