This makes use of the iPXE sanboot command [1] which downloads and
boots an ISO image directly via HTTP. Therefore, your RUN_OPT needs
both
--include image/iso and
--include load/ipxe
NOTE: The webserver serving the ISO image must support ranged requests,
see [2].
[1] - http://ipxe.org/cmd/sanboot
[2] - http://forum.ipxe.org/showthread.php?tid=7295&pid=10482#pid10482