Convert bridge driver over to use new firewall APIs

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>