Get IPTables rules present on server

Collects IPTables data from server.

Sample output:

```
$ out/Debug/rackspace-monitoring-agent -e hostinfo_runner.lua -d -x IPTABLES
HostInfo Running IPTABLES
Serialized Results:
{
    "metrics": [
        "-P INPUT ACCEPT",
        "-P FORWARD ACCEPT",
        "-P OUTPUT ACCEPT",
        "-N fail2ban-ssh",
        "-A INPUT -p tcp -m tcp --dport 8080 -j ACCEPT",
        "-A INPUT -p tcp -m multiport --dports 22 -j fail2ban-ssh",
        "-A fail2ban-ssh -j RETURN"
    ],
    "timestamp": 1410293443053
}
```