Ganeti support

Hello jfried,

This patch extends Rex's cloud functionnality to support for Ganeti [1]

It uses its RAPI interface to handle basic VM instance handling. There is some work left to do, to support most advanced Ganeti features.

Warning : This Ganeti module won't setup Ganeti for you, you *need* a working install. 

This is a Work in Progress, you can use it for create, list, stop, remove a VM.

This module is largely inspired by the OpenNebula module, so I put credit where credit is due :)

Cheers !

[1] https://code.google.com/p/ganeti/