[gPXE] Only register bios drive without booting

[Miller, Shao]

Andrey,

In regards to your attempts to SAN-boot an HDD which had Windows 7
installed on it while there were two disks attached to the system:

Windows most likely boot the booting system on whichever HDD it deemed
as the "first" HDD, even if it installed Windows 7 to your "second" HDD.

The simplest thing to do is
- to have one HDD in the computer system
- installed Windows 7 to it
- make sure networking is fully functional
- make sure an iSCSI test succeeds to validate your iSCSI target setup
- remove the HDD and either attach it to your iSCSI target system or
take a raw HDD image and serve that from the iSCSI target system

- Shao Miller