Add EFI support and Grub bootloader

[kvaps]

Hi, I had some experience for adding UEFI support.
I've tried few different configurations.

1) The first one uses classic pxelinux.cfg configuration just adds syslinux.efi bootloader to /boot path.
The syslinux uses internal efi functions for download image, and I was surprised that TFTP download works much slow in my system, but HTTP download works really fine.
So I've also added lpxelinux.0 bootloader to path, and SERVER_PREFIX option for allow using HTTP-server for holding kernel images.
Unfortunately, I have some problems with using lpxelinux.0 bootloader on my non-EFI system.

2) Another case is using grub bootloader. I've tried it and found that it is working really amazing and very simmilar on any systems (EFI and non-EFI)
So I've switched to using grub instead pxelinux/syslinux.
I've changed server's ltsp-update-kernel script for automatically generate grub configuration, and install it into right ltsp prefix. I think that host's evironment is better place for holding bootloader than chrooted environment, because you don't need to have installed packages there, so make it smaller.
In this case, if you don't use pxelinux you don't need to call clinet's update-kernels script anymore.

My achievements are saved in github:

Syslinux enhancement: https://github.com/kvaps/ltsp/tree/feature-efi
Grub bootloader support: https://github.com/kvaps/ltsp/tree/feature-grub

I'm adding following patches into this topic.

Thank you!

[Alkis Georgopoulos (alkisg)]

Closing old LTSP bugs as they're no longer relevant after LTSP has been rewritten from scratch.