goal: `oc create` of MachineConfig continues to work; all our existing e2e tests pass, and representative QE custom MachineConfig continues to work.

Acceptance criteria: when MachineConfigs are applied, all MachineConfig fields supported by rpm-ostree and ignition-liveapply are applied in a container image. An administrator (and QE etc.) can find, pull and run the derived container image and see their changes inside. There is at least minimal available documentation about the relevant internals changes (e.g. BuildConfig) and these are visible.

(stretch) AC: Can apply the hotfix

Anything not supported by rpm-ostree and ignition-liveapply is still correctly applied by the MCD