Allow user to specify nic interface to be taken into /etc/hosts file

Hi Shawn,

I'm proposing new feature to allow user to use nic interface in order to resolve ip address.
The reason behind is following, in my case when creating new nodes in eucalyptus cloud 
vagrant machine.ssh_info[:host] = public dns name (which is different that private ip)
and this causes problems in ubuntu, because in /etc/hosts you can only have ip addresses.

Let me know what do You think?
For me this change works great, because in case of euca cloud I can point to nic which is considered to be private ip, so guests can see each other without any problems, the same story in rackspace, and last but not least in virtualbox (using bridged networks) u could also point to specific nic to be resolved, rather than rely on ssh_info (because it's 127.0.0.1)