should remove dependancy on /etc/environment

[peebs]

This file isn't create when ignition is used over cloud-config. Right now it fills in the ADVERTISE_IP env in the generic and single-node scripts.

We should be get our info from the metadata service and possibly add some platform specific logic here to make these scripts truly more generic. For example, for the generic scripts to work on GCE out of the box one must s/COREOS_PUBLIC_IPV4/COREOS_PRIVATE_IPV4 to the scripts.

https://coreos.com/ignition/docs/latest/metadata.html

cc @crawford