[libvirt] Add vncdisplay to virsh list

[Дмитрий Ильин]

I think adding vncdisplay to virsh list output will be very usefull.

For example output could be like this:

 Id Name                 State              Display
----------------------------------------------------
 1 test1                running              :2
 2 test2                running              :5
 3 test3                running              :13
 4 server1              running              n/g
 5 sdltest              running              sdl
 - test4                shut off             off
 - test5                shut off             off

:n - vnc display number
n/g - no graphics
sdl - sdl output

You can use "--display" to enable it

command:
virsh list --all --display


Also I would like to see "--pretend" option in virt-install.
Just generate xml and dump it to stdout without doing anything else.