Rename container-linux modules to flatcar-linux

* CoreOS Container Linux was deprecated in v1.18.3
* Continue transitioning docs and modules from supporting
both CoreOS and Flatcar "variants" of Container Linux to
now supporting Flatcar Linux and equivalents

Action Required: Update the Flatcar Linux modules `source`
to replace `s/container-linux/flatcar-linux`. See docs for
examples

google-cloud/flatcar-linux/kubernetes/workers/cl/worker.yaml

@@ -0,0 +1,115 @@
+---
+systemd:
+  units:
+    - name: docker.service
+      enabled: true
+    - name: locksmithd.service
+      mask: true
+    - name: wait-for-dns.service
+      enabled: true
+      contents: |
+        [Unit]
+        Description=Wait for DNS entries
+        Wants=systemd-resolved.service
+        Before=kubelet.service
+        [Service]
+        Type=oneshot
+        RemainAfterExit=true
+        ExecStart=/bin/sh -c 'while ! /usr/bin/grep '^[^#[:space:]]' /etc/resolv.conf > /dev/null; do sleep 1; done'
+        [Install]
+        RequiredBy=kubelet.service
+    - name: kubelet.service
+      enabled: true
+      contents: |
+        [Unit]
+        Description=Kubelet
+        Requires=docker.service
+        After=docker.service
+        Wants=rpc-statd.service
+        [Service]
+        Environment=KUBELET_IMAGE=quay.io/poseidon/kubelet:v1.19.3
+        ExecStartPre=/bin/mkdir -p /etc/kubernetes/cni/net.d
+        ExecStartPre=/bin/mkdir -p /etc/kubernetes/manifests
+        ExecStartPre=/bin/mkdir -p /opt/cni/bin
+        ExecStartPre=/bin/mkdir -p /var/lib/calico
+        ExecStartPre=/bin/mkdir -p /var/lib/kubelet/volumeplugins
+        ExecStartPre=/usr/bin/bash -c "grep 'certificate-authority-data' /etc/kubernetes/kubeconfig | awk '{print $2}' | base64 -d > /etc/kubernetes/ca.crt"
+        # Podman, rkt, or runc run container processes, whereas docker run
+        # is a client to a daemon and requires workarounds to use within a
+        # systemd unit. https://github.com/moby/moby/issues/6791
+        ExecStartPre=/usr/bin/docker run -d \
+          --name kubelet \
+          --privileged \
+          --pid host \
+          --network host \
+          -v /etc/kubernetes:/etc/kubernetes:ro \
+          -v /etc/machine-id:/etc/machine-id:ro \
+          -v /usr/lib/os-release:/etc/os-release:ro \
+          -v /lib/modules:/lib/modules:ro \
+          -v /run:/run \
+          -v /sys/fs/cgroup:/sys/fs/cgroup:ro \
+          -v /sys/fs/cgroup/systemd:/sys/fs/cgroup/systemd \
+          -v /var/lib/calico:/var/lib/calico:ro \
+          -v /var/lib/docker:/var/lib/docker \
+          -v /var/lib/kubelet:/var/lib/kubelet:rshared \
+          -v /var/log:/var/log \
+          -v /opt/cni/bin:/opt/cni/bin \
+          $${KUBELET_IMAGE} \
+          --anonymous-auth=false \
+          --authentication-token-webhook \
+          --authorization-mode=Webhook \
+          --bootstrap-kubeconfig=/etc/kubernetes/kubeconfig \
+          --client-ca-file=/etc/kubernetes/ca.crt \
+          --cluster_dns=${cluster_dns_service_ip} \
+          --cluster_domain=${cluster_domain_suffix} \
+          --cni-conf-dir=/etc/kubernetes/cni/net.d \
+          --healthz-port=0 \
+          --kubeconfig=/var/lib/kubelet/kubeconfig \
+          --network-plugin=cni \
+          --node-labels=node.kubernetes.io/node \
+          %{~ for label in split(",", node_labels) ~}
+          --node-labels=${label} \
+          %{~ endfor ~}
+          --pod-manifest-path=/etc/kubernetes/manifests \
+          --read-only-port=0 \
+          --rotate-certificates \
+          --volume-plugin-dir=/var/lib/kubelet/volumeplugins
+        ExecStart=docker logs -f kubelet
+        ExecStop=docker stop kubelet
+        ExecStopPost=docker rm kubelet
+        Restart=always
+        RestartSec=5
+        [Install]
+        WantedBy=multi-user.target
+    - name: delete-node.service
+      enabled: true
+      contents: |
+        [Unit]
+        Description=Delete Kubernetes node on shutdown
+        [Service]
+        Environment=KUBELET_IMAGE=quay.io/poseidon/kubelet:v1.19.3
+        Type=oneshot
+        RemainAfterExit=true
+        ExecStart=/bin/true
+        ExecStop=/bin/bash -c '/usr/bin/docker run -v /var/lib/kubelet:/var/lib/kubelet:ro --entrypoint /usr/local/bin/kubectl $${KUBELET_IMAGE} --kubeconfig=/var/lib/kubelet/kubeconfig delete node $HOSTNAME'
+        [Install]
+        WantedBy=multi-user.target
+storage:
+  files:
+    - path: /etc/kubernetes/kubeconfig
+      filesystem: root
+      mode: 0644
+      contents:
+        inline: |
+          ${kubeconfig}
+    - path: /etc/sysctl.d/max-user-watches.conf
+      filesystem: root
+      mode: 0644
+      contents:
+        inline: |
+          fs.inotify.max_user_watches=16184
+passwd:
+  users:
+    - name: core
+      ssh_authorized_keys:
+        - "${ssh_authorized_key}"