s390x: add Butane config for creating GenprotimgVM locally

This template coul be used to create genprotimgvm locally. During
build this VM is used to generete 'sdboot' image and 'zipl' it on
coreos.qemu-secex.s390x.qcow2 image.

Put this template, your id_rsa.pub and valid secex-hostkey into
same directory and generate Ignition config:
```
butane --pretty --files-dir . genprotimg.bu -o genprotimg.ign
```

Than get rhcos.qemu-secex.s390x.qcow2 and customize it with
generated above ignition config.

Author: nikita-dubrovskii

src/secex-genprotimgvm-scripts/genprotimg.bu

@@ -0,0 +1,75 @@
+variant: fcos
+version: 1.5.0
+passwd:
+  users:
+    - name: core
+      ssh_authorized_keys_local:
+        - id_rsa.pub
+      groups:
+        - wheel
+storage:
+  directories:
+    - path: /var/genprotimg
+    - path: /var/build
+  files:
+    - path: /etc/se-hostkeys/ibm-z-hostkey-1
+      overwrite: true
+      contents:
+        local: secex-hostkey
+    - path: /etc/do_genprotimg
+      overwrite: true
+      mode: 0755
+      contents:
+        inline: |
+          #!/bin/bash
+          set -euo pipefail
+          trap "rm -f /var/genprotimg/signal.file" EXIT
+          bash /var/build/genprotimg-script.sh &
+          while [ ! -e "/var/genprotimg/signal.file" ]; do
+              sleep 1
+          done
+          genprotimg -V --no-verify -i /var/genprotimg/vmlinuz -r /var/genprotimg/initrd.img  -p /var/genprotimg/parmfile -k /etc/se-hostkeys/ibm-z-hostkey-1 -o /var/genprotimg/se.img
+          rm -f /var/genprotimg/signal.file
+          bash /var/build/post-script.sh
+systemd:
+  units:
+    - name: [email protected]
+      dropins:
+        - name: autologin-core.conf
+          contents: |
+            [Service]
+            TTYVTDisallocate=no
+            ExecStart=
+            ExecStart=-/usr/sbin/agetty --autologin core  -o '-p -f core' --noclear %I $TERM
+      mask: false
+    - name: [email protected]
+      mask: false
+    - name: genprotimg.service
+      enabled: true
+      contents: |
+        [Unit]
+        Description=GenProtImg
+        ConditionKernelCommandLine=!ignition.firstboot
+        After=var-build.mount
+        [Service]
+        Type=oneshot
+        StandardOutput=journal+console
+        ExecStart=/etc/do_genprotimg
+        ExecStopPost=/sbin/halt
+        [Install]
+        WantedBy=default.target
+    - name: var-build.mount
+      enabled: true
+      contents: |
+        [Unit]
+        Description=Mounts genprotimg build partition
+        ConditionKernelCommandLine=!ignition.firstboot
+        Requires=dev-disk-by\x2did-virtio\x2dgenprotimg.device
+        After=dev-disk-by\x2did-virtio\x2dgenprotimg.device
+        [Mount]
+        What=/dev/disk/by-id/virtio-genprotimg
+        Where=/var/build
+        Type=ext4
+        Options=rw,noatime
+        [Install]
+        WantedBy=default.target