Network related changes

Based on our conversation yesterday, I've done two things:

1) There's a public and a private network interface on every node. To me, that implies the private is a non-routable network, so we shouldn't be supplying a gateway from the DHCP server. The first commit deals with necessary changes to the foreman-installer (already merged upstream).

2) We need to know some a-priori information about the network, especially the IP of the controller node (for use in the manifests). I've made the assumption that the Foreman server will have IP = $NETWORK.2 and the controller will have $NETWORK.3. The second commit deals with sed'ing those values into the manifests before the Puppet module import.