Data bag support

Can you check my pull request? It adds data bag support to iptables-ng, in my case it very usefl. I'm add databags via node attributes like:
```
                    "iptables-ng" => {
                      "data_bag_name" => "firewall",
                      "data_bags" => [ "default", "relay_kh", "netflow_kh", "ospf", "vncproxy", "ssh", "vps_kh", "corosync" ]
                    },
```

And in each databag i have
```
{
    "id": "ospf",
    "rules": {
        "filter": {
            "INPUT": {
                "ospf": {
                    "rule": "-s 10.220.0.0/16 -d 224.0.0.5/30 -p 89 -j ACCEPT",
                    "ip_version": 4
                }
            }
        }
    }
}
```