[libvirt] disk XML for error policy

[Dave Allan]

Hi Dan,

What do you think of this for the disk XML specifying what to do on error:

     <disk type='file' device='disk'>
       <source file='/storage/guest_disks/libgdu'/>
       <target dev='vda' bus='virtio'/>
       <on_err rerror='stop' werror='stop'/>
     </disk>

Dave