* Detect CoreOS
* Move key manifests to code, to tolerate read-only mounts
* Misc refactorings so more code can be shared
* Change lots of ints to int32s in the models
* Run nodeup as a oneshot systemd service, rather than relying on
cloud-init behaviour which varies across distros
* Always read /etc/redhat-release (symlinked on CentOS)
* Make _rhel_family the tag name, not _centos_family
* Add comment about writing to "system" systemd area
The idea being we don't necessarily always want to pick up the latest
change immediately, without validating it first.
Also this is an easy way to recommend the latest AMI without having to
search for it. We also create an alias to the owner id, so that it is
readable / verifiable.