Updated installation instructions for Ubuntu

[Robert Markula]

Hey guys,

I would like to update the Wiki page on Ubuntu [1] with instructions on
how to install and run FAI 4.2.4 on Ubuntu 14.04 using a Ubuntu 14.04
NFSroot and installing Ubuntu 14.04 on the clients.
The current information about Ubuntu 12.04 is deprecated (12.04 is still
supported but the current LTS is 14.04) and partly incorrect. Would that
be okay with you?

Also, I managed to get FAI 4.2.4 working on Ubuntu 14.04 using a *Debian
Wheezy* NFSroot and installing Ubuntu 14.04 on the clients. Is there any
need for this constellation?

It would be great if some of you could help me testing the instructions
once they are published.

Cheers,

Robert

[1] http://wiki.fai-project.org/wiki/Installing_Ubuntu_Linux_with_FAI