include generic.ins for s390 boot iso

Include the generic.ins file on the s390 boot iso, so it's directly bootable
on an LPAR. The full iso already had generic.ins included.

(cherry picked from commit 0dbfe28745)
Signed-off-by: Brian C. Lane <bcl@redhat.com>

Related: rhbz#1844517

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

@@ -72,6 +72,7 @@ runcmd mkisofs -o ${outroot}/images/boot.iso \
        -b ${BOOTDIR}/cdboot.img -c ${BOOTDIR}/boot.cat \
        -boot-load-size 4 -no-emul-boot \
        -R -J -V '${isolabel}' -T -graft-points \
+       generic.ins=${outroot}/generic.ins \
        ${BOOTDIR}=${outroot}/${BOOTDIR} \
        ${filegraft}
 treeinfo images-${basearch} boot.iso images/boot.iso