Convert bridge driver over to use new firewall APIs
    
    Update the iptablesXXXX methods so that instead of directly
    executing iptables commands, they populate rules in an
    instance of virFirewallPtr. The bridge driver can thus
    construct the ruleset and then invoke it in one operation
    having rollback handled automatically.
    
    Signed-off-by: Daniel P. Berrange <berrange@redhat.com>