[gPXE] About using WinPE

[Miller, Shao]

Good day again Ozan,

The point is that your SAN should have its MBR zeroed out.  keep-san
will tell gPXE "try to SAN-boot, but if that fails, leave the SAN
connected and leave the SAN params in memory, for a later OS to find, if
needed."

The zeroed MBR will return you to gPXE, from which you then chain the
Windows NBP.

Windows' iSCSI support will find the SAN params in memory and attach the
SAN.

- Shao Miller