This still isn't working at the moment. See:
http://marc.info/?t=139457409300003&r=1&w=2
This set of patches:
- Adds new APIs to support discard in libguestfs.
- Adds discard support to virt-format.
- Adds discard support to virt-sysprep.
- Implements virt-sparsify --in-place.
Rich.