Accept parameter values with whitespace.

E.g. the tcp match extension uses --tcp-flags in this way:

    # iptables -I INPUT -p 23 -m tcp --tcp-flags ACK SYN -j REJECT

Parameters like this need to be passed quoted in python-iptables:

    >>> rule.create_match("tcp")
    >>> match.tcp_flags = "\"ACK SYN\""
Update comment test to quote parameter value.