Review adding Ignition support for CoreOS to cross-cloud

[lixuna]

Reason: cloud-init support is deprecated in CoreOS

Reference: https://github.com/coreos/coreos-cloudinit

[akutz]

Hi @lixuna,

A minor point: cloud-init is deprecated in CoreOS. It will (if CoreOS follows standard rules) eventually be removed entirely.

NOTE: This project has been superseded by Ignition and is no longer under active development. Please direct all development efforts to Ignition.