Add creation of a bootable s390 iso (#1478448)

Use mk-s390-cdboot to create a combined kernel+initrd and then build a
boot.iso using it.

share/templates.d/99-generic/config_files/s390/cdboot.prm

@@ -0,0 +1 @@
+ro

share/templates.d/99-generic/s390.tmpl

@@ -19,6 +19,7 @@ treeinfo stage2 mainimage images/${runtime_base}
 install ${configdir}/redhat.exec ${BOOTDIR}
 install ${configdir}/generic.prm ${BOOTDIR}
 install ${configdir}/genericdvd.prm ${BOOTDIR}
+install ${configdir}/cdboot.prm ${BOOTDIR}
 install ${configdir}/generic.ins .
 
 ## configure bootloader
@@ -59,3 +60,18 @@ treeinfo images-${basearch} generic.ins generic.ins
     install ${f} ${f|basename}
     <% filegraft += " {0}={1}/{0}".format(basename(f), outroot) %>
 %endfor
+
+## Make a combined kernel+initrd image for the iso
+runcmd mk-s390-cdboot -i ${outroot}/${KERNELDIR}/kernel.img \
+                      -r ${outroot}/${KERNELDIR}/initrd.img \
+                      -p ${outroot}/${BOOTDIR}/cdboot.prm \
+                      -o ${outroot}/${BOOTDIR}/cdboot.img
+
+## make boot.iso
+runcmd mkisofs -o ${outroot}/images/boot.iso \
+       -b ${BOOTDIR}/cdboot.img -c ${BOOTDIR}/boot.cat \
+       -boot-load-size 4 -boot-info-table -no-emul-boot \
+       -R -J -V '${isolabel}' -T -graft-points \
+       ${BOOTDIR}=${outroot}/${BOOTDIR} \
+       ${imggraft}
+treeinfo images-${basearch} boot.iso images/boot.iso