Add iPXE/static-boot support for Debian

Tested with this procedure:

* Created a network in libvirt with no DHCP
* Created a BareMetal Host if Foreman with an IP on this network
* Booted a libvirt vm using the vanilla iPXE kernel (ipxe.iso) from ipxe.org
* Manually entered netX/ip, netX/gateway, dns params
* Chainloaded the iPXE template, leading to the modified static provison

Seems to work on Wheezy, not tested the others. Going to try and fix the bootdisk plugin for easier testing :P