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
coreos-base/oem-rackspace-teeth: Force network interfaces to simple names

Rackspace teeth depends on the original (eth0, eth1) kernel names. Add a new
default networkd link file that disables the persistant names.