Links v2: Mutable network files

This exploits the new MS_SLAVE support in libcontainer to make `/etc/resolv.conf` and `/etc/hosts` mutable.

This also fixes the /etc/hosts test and adds a few of its own.

Caveat: restarting a container (currently) does not keep /etc/hosts intact. I'm still torn on whether this is a feature or not.
Hell, now this is unreadable at all :) Could you pls change to named fields?