added debuglevel to ohai ipaddress call

On my ec2 instance ( Ubuntu 12.04.1 LTS ), the *ohai* command sends an additional info output, which breaks _get_ipaddess()

```shell
ubuntu@ip-10-11-12-123:~$ ohai ipaddress
[Mon, 21 Jan 2013 09:28:28 +0000] INFO: [inet6] no default interface, picking the first ipaddress
[
  "10.11.12.123"
]
```
Adding *-l warn* suppresses this.