Update to vmfusion ip.rb helper to retrieve IPs for bridged networks in addition to NAT and host-only

The current code can only retrieve NAT or host-only IPs by polling nat/dhcp settings. This means that a box that is configured for bridged networking isn't accessible with the "veewee fusion ssh <boxname>" command. By using vmrun's guestVar command instead it's possible to retrieve IPs in all networking setups.

I have successfully tested with OS X and CentOS 6.3 guests so far.

Note: this is probably woefully dirty code but it does the job for now. Feel free to clean it up as needed.