GCE guidelines adherence (unfinished)

I have implemented a lot of the guidelines: https://developers.google.com/compute/docs/images#buildingimage

There are things that remain but, for now, it works fine. Some outstanding things pending are:
* Install Google things: https://github.com/GoogleCloudPlatform/compute-image-packages
* Configure ssh as they want it too
They ask you to use their own ntp server. I didn't know systemd provided ntp. Where do you configure the servers for that?