No RHCOS image in baremetal Machines and MachineSets

[markmc]

In the Generate() function for masters and workers under pkgs/assets/machines every other platform except libvirt generates an RHCOS image asset and includes it in the Machines or MachineSets it generates

Why isn't the baremetal platform doing this?

(NB - currently on baremetal the generated RHCOS image is the qcow image we use with libvirt for the bootstrap VM. If we were to include bootimage info in the generated machine manifests, we would need to make it have the proper URL instead)

[markmc]

Some of the underlying assumptions of the rhcos.Image abstraction:

1. The same image is used for bootstrap, masters, and workers
2. That image information is included in the generated machines manifests and also to terraform

I think we should follow that basic idea and just have an "oh hey, our bootstrap node boot image is different!" special case

[markmc]

Moved to openshift/installer#2037