coreos-base/oem-rackspace-teeth: Make cloudinit drop-in an actual unit

This will guarentee that cloudinit reloads systemd's unit files.
Also, fix the ordering on the config-drive mount.
coreos-base/oem-rackspace-teeth: Add pingout service
networkd: Emulate old kernel naming

The old kernel names are handed out by netname.sh which is called by
79-netname.rules. rename-network-interfaces.service does the rename by
stopping networkd, taking down the interfaces, re-adding the interfaces,
and then restarting networkd.
Merge pull request #730 from crawford/teeth

coreos-base/oem-rackspace-teeth: Add support for network