Adding libvirt setup scenario

Do not merge yet - preview.

It looks like hammer is not yet ready for complete scenario.
> > +  hammer -d medium add-operatingsystem --id 1 --operatingsystem-id 1
> > +  hammer -d medium add-operatingsystem --id 7 --operatingsystem-id 1
> 
> Maybe we could at least put them in a variable? I'd prefer reading ```$OS_REDHAT``` instead of ```1``` (or whatever OS that is).

I agree, I'd like to improve the script as CLI support improves rather
than trying to achieve everything today. This seems to be a good
starting point - sure CentOS is hardcoded here.

-- 
Later,
 Lukas #lzap Zapletal