[libvirt] Changing the default for qcow2 creation

[Justin Clift]

On 10/26/2010 01:06 AM, Richard W.M. Jones wrote:
<snip>
>> 4. A metadata preallocated qcow2 file:		 14.5 seconds
>>     qemu-img create -f qcow2 -o preallocated=metadata test.img 300M

Just tested this on a F13 host, and it didn't like the the preallocated
option:

  $ qemu-img create -f qcow2 -o preallocated=metadata testvm.qcow2 20G
  Unknown option 'preallocated'
  qemu-img: Invalid options for file format 'qcow2'.
  $

Looks like we'd need to add some kind of testing for the capability
first. :)