Various cleanups for CoreOS-related things (openshift#59000)

* openshift/os: simplify image definitions

First, stop using the `fcos-buildroot` image. It's no longer defined in
this repo and we don't strictly need it.

Instead, use cosa as the buildroot. This then allows us to get rid of
the redundant `base_images` definition, and use the `root` image as our
`from`.

Use `FROM overridden` in the Dockerfile literal to make it clear that
it's always going to be overridden anyway.

* openshift/os: no longer limit tests to build02

As per openshift/os#1551 (comment)
we should no longer have to limit tests to the build02 cluster since
OpenShift CNV was installed on all the build clusters.

This should make it easier for our jobs to get scheduled.

* openshift/os: nuke configs for branches < 4.12

We don't care about those branches anymore and they should not be
receiving any new content.

* image-mirroring: stop mirroring coreos-assembler for releases < 4.12

We don't care about those tags anymore and they should no longer be
used.

* supplemental-ci-images: drop unused images and buildconfigs

We ended up not really using these images. Just delete them. We can
always readd those we need in the future.

* openshift/os: drop COSA_SKIP_OVERLAY=1 workaround

This is no longer required after:

coreos/coreos-assembler#3936

* core-services/image-mirroring: Mirror 4.18 image for COSA

* ci-operator/openshift/os: 4.18 use 4.18 cosa

* ci-operator/coreos/coreos-assembler: Add CI for 4.18 branch

* openshift/os: drop testing of SCOS and RHCOS 9.6 on 4.18

These are no longer relevant for 4.18, so nuke them.

---------

Co-authored-by: Michael Nguyen <[email protected]>

Author: 2 people

ci-operator/config/coreos/coreos-assembler/coreos-coreos-assembler-rhcos-4.18.yaml

@@ -0,0 +1,31 @@
+build_root:
+  project_image:
+    dockerfile_literal: |
+      FROM quay.io/fedora/fedora:40
+      RUN dnf install -y git findutils
+      RUN mkdir /go && chmod 777 /go
+images:
+- dockerfile_path: Dockerfile
+  from: root
+  to: bin
+resources:
+  '*':
+    requests:
+      cpu: 1000m
+      memory: 1Gi
+  rhcos:
+    limits:
+      devices.kubevirt.io/kvm: "1"
+    requests:
+      cpu: 1000m
+      devices.kubevirt.io/kvm: "1"
+      memory: 3Gi
+tests:
+- as: rhcos
+  commands: /usr/lib/coreos-assembler/ci/prow-rhcos.sh
+  container:
+    from: bin
+zz_generated_metadata:
+  branch: rhcos-4.18
+  org: coreos
+  repo: coreos-assembler

ci-operator/config/openshift/os/openshift-os-master.yaml

@@ -1,23 +1,15 @@
-base_images:
-  coreos_coreos-assembler_latest:
-    name: coreos-assembler
-    namespace: coreos
-    tag: latest
 build_root:
   image_stream_tag:
-    name: fcos-buildroot
+    name: coreos-assembler
     namespace: coreos
-    tag: testing-devel
+    tag: latest
 images:
 - dockerfile_literal: |
-    # COSA + source code
-    FROM registry.ci.openshift.org/coreos/coreos-assembler:latest
+    FROM overridden
     WORKDIR /src
     # Tell the build scripts that we have setup a directory for unprivileged build
     ENV COSA_DIR=/tmp/cosa
     RUN mkdir -p "${COSA_DIR}"
-    # Prow doesn't support emptydir for jobs today
-    ENV COSA_SKIP_OVERLAY=1
     # Copy the source code
     COPY . .
     # We need to make sure that root can read / write to the COSA_DIR so that
@@ -29,10 +21,7 @@ images:
     # Go back to unprivileged user for COSA
     USER builder
     WORKDIR /tmp/cosa
-  inputs:
-    coreos_coreos-assembler_latest:
-      as:
-      - registry.ci.openshift.org/coreos/coreos-assembler:latest
+  from: root
   to: build-image
 promotion:
   to:
@@ -118,56 +107,48 @@ tests:
     from: src
   skip_if_only_changed: ^docs/|\.md$|^(?:.*/)?(?:\.gitignore|OWNERS|PROJECT|LICENSE)$
 - as: rhcos-9-build-test-qemu
-  cluster: build02
   commands: /src/ci/prow-entrypoint.sh rhcos-9-build-test-qemu
   container:
     from: build-image
   skip_if_only_changed: ^docs/|\.md$|^(?:.*/)?(?:\.gitignore|OWNERS|PROJECT|LICENSE)$
   timeout: 4h0m0s
 - as: rhcos-9-build-test-metal
-  cluster: build02
   commands: /src/ci/prow-entrypoint.sh rhcos-9-build-test-metal
   container:
     from: build-image
   skip_if_only_changed: ^docs/|\.md$|^(?:.*/)?(?:\.gitignore|OWNERS|PROJECT|LICENSE)$
   timeout: 3h0m0s
 - as: rhcos-96-build-test-qemu
-  cluster: build02
   commands: /src/ci/prow-entrypoint.sh rhcos-96-build-test-qemu
   container:
     from: build-image
   skip_if_only_changed: ^docs/|\.md$|^(?:.*/)?(?:\.gitignore|OWNERS|PROJECT|LICENSE)$
   timeout: 4h0m0s
 - as: rhcos-96-build-test-metal
-  cluster: build02
   commands: /src/ci/prow-entrypoint.sh rhcos-96-build-test-metal
   container:
     from: build-image
   skip_if_only_changed: ^docs/|\.md$|^(?:.*/)?(?:\.gitignore|OWNERS|PROJECT|LICENSE)$
   timeout: 3h0m0s
 - as: scos-9-build-test-qemu
-  cluster: build02
   commands: /src/ci/prow-entrypoint.sh scos-9-build-test-qemu
   container:
     from: build-image
   skip_if_only_changed: ^docs/|\.md$|^(?:.*/)?(?:\.gitignore|OWNERS|PROJECT|LICENSE)$
   timeout: 4h0m0s
 - as: scos-9-build-test-metal
-  cluster: build02
   commands: /src/ci/prow-entrypoint.sh scos-9-build-test-metal
   container:
     from: build-image
   skip_if_only_changed: ^docs/|\.md$|^(?:.*/)?(?:\.gitignore|OWNERS|PROJECT|LICENSE)$
   timeout: 3h0m0s
 - as: scos-10-build-test-qemu
-  cluster: build02
   commands: /src/ci/prow-entrypoint.sh scos-10-build-test-qemu
   container:
     from: build-image
   skip_if_only_changed: ^docs/|\.md$|^(?:.*/)?(?:\.gitignore|OWNERS|PROJECT|LICENSE)$
   timeout: 4h0m0s
 - as: scos-10-build-test-metal
-  cluster: build02
   commands: /src/ci/prow-entrypoint.sh scos-10-build-test-metal
   container:
     from: build-image