WIP: networker skeleton

worker: networker skeleton

This RP is a skeleton for the future networker based on StringsWorker

Continue of work from: https://github.com/juju/juju/pull/86
I need to configure interfaces in /etc/network/interfaces in order to use ifup utility. Method interfaceIsConfigured only verifies whether interface is configured inside that file. I use net package to figure out if interface is up and has an IP address.