import_raw_vdi: use vhd-tool helper program

The vhd-tool helper is capable of O_DIRECT I/O and minimises
data copies.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
import_raw_vdi: log output from vhd-tool

This can be useful in diagnosing errors.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
HFX-990: Revert to using Uuid instead of Uuidm

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
HFX 990: Correct vhd-tool path for 6.0.2 backport

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>