Return an appropriate WSGI server class base on provided host
        :param host: The listen host for the zaqar API server.

def _get_server_cls(self, host):
        """Return an appropriate WSGI server class base on provided host
        :param host: The listen host for the zaqar API server.
        """
        server_cls = simple_server.WSGIServer
        if netutils.is_valid_ipv6(host):
            if getattr(server_cls, 'address_family') == socket.AF_INET:
                class server_cls(server_cls):
                    address_family = socket.AF_INET6
        return server_cls