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
Also, looking at the code below, it seems you can do:
`ifaces map[string]net.Interface`
here, and convert the slice to the map using the interface name as key. This way you can do trivial lookups for "is it up", "does it have an address", etc.