[gPXE] Machines hangs when exiting from CLI

[Miller, Shao]

Good day Jon

In regards to the gPXE CLI during POST:

A gPXE .ROM build target flashed to a NIC's ROM (or otherwise properly
incorporated into a BIOS image) will yield three prompts during computer
startup.

The first prompt is a Control-B prompt from
gpxe/src/arch/i386/prefix/romprefix.S.  Since POST has not yet completed
(we're simply an initializing ROM), the environment is not guaranteed
fully setup.  Some models have been observed to have a non-existent,
bogus, or incorrect E820 map, for example.

The next is from the same file and prompts to press N to skip booting
from gPXE.

The last is the usual post-POST Control-B prompt from
gpxe/src/hci/shell_banner.c.

You can incorporate a gPXE ROM into QEmu or VirtualBox or VMware, using
the details at http://www.etherboot.org/wiki/romburning and
http://www.etherboot.org/wiki/vmwarebios

- Shao Miller