Flushes the specified chain (all the chains in the table if
        none is given). This is equivalent to deleting all the rules
        one by one.

def flush_chain(self, chainname=None):
        """Flushes the specified chain (all the chains in the table if
        none is given). This is equivalent to deleting all the rules
        one by one.
        """
        args = ['-F']
        if chainname: args.append(chainname)
        self.__run_iptables(args)