PXE boot option to run memtest86+

[jabl]

Like #10 , it would be nice to have a way to alternatively PXE boot memtest86+ in order to troubleshoot a node.

[martbhell]

http://forum.ipxe.org/showthread.php?tid=7937 seems to be doable

[martbhell]

In CSCfi/ansible-role-dhcp-kickstart#10 (which has another fork of this boot.py that does not (yet) use the json improvements done in this repo) I have gotten something that works for BIOS boots.

memtest.0 was found here: http://forum.ipxe.org/showthread.php?tid=7937&highlight=memtest

This will probably not work for servers that boot with UEFI though and I don't have such a system to test with.

The resulting iPXE config:

#!ipxe
kernel http://webserver/memtest.0
boot