ipatests/test_integration/test_http_kdc_proxy.py: Use new firewall import
    
    Instead of using ip[6]tables commands, use new firewall class to deny
    access to TCP and UDP port 88 on external machines using the OUTPUT chain.
    The iptables calls in the install method are replaced by a
    prepend_passthrough_rules call with the rules defined in the class.
    
    The firewall rules are defined in the class as fw_rules without
    --append/-A, --delete/-D, .. First entry of each rule is the chain name,
    the argument to add or delete the rule will be added by the used Firewall
    method. See firewall.py for more information.
    
    The "iptables -F" call (IPv4 only) in the uninstall method is replaced by
    a remove_passthrough_rules call with the rules defined in the class.
    
    See: https://pagure.io/freeipa/issue/7755
    Signed-off-by: Thomas Woerner <twoerner@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Armando Neto <abiagion@redhat.com>