when defining Zero-OS as first boot, we can not get the node back
into rescue mode as that is the way Hetzner functions:
tne netboot get an ipxe that doe a local reload or, in case of rescue
starts a full netboot

removed zos-on-hetzner as it's more generic
added zosinstalluefipxeondisk.sh as generic isntall script
  to install the bootblock on a node's disk
  select zos4 as main driver for zos