CimFS layers don't need to create a new scratch VHD per image. The scratch VHDs used with CimFS are empty so
we can just create one base VHD and one differencing VHD and copy it for every scratch snapshot.
(Note that UVM VHDs are still unique per image because the VHD information is embedded in the UVM BCD during
import)
Signed-off-by: Amit Barve <ambarve@microsoft.com>
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