Fix initial buildconfigs: the builder, base and forked-dockerfiles must not depend on images that will be built during their batch execution or later.
Fix TAGS patches for the fcos-multiarch variant's overlay: explicitly set the TAGS for installer and mco in the fcos-multiarch variant to fcos libvirt baremetal for the baremetal-installer and fcos for the other components requesting it.
Fix the fedora-coreos artifacts image replacement for 4.15: use origin:4.15 as base
New replacements for 4.15: adds the replacement for the builder and base images
No patch for the branch to build in the kustomization.yaml: prefer a hard-coded release branch vs a kustomization patch
This PR is split from #50:
fcos-multiarchvariant tofcos libvirt baremetalfor the baremetal-installer andfcosfor the other components requesting it.