Fix wrapped error missing when failing to add scratch VHD
Fix wrapped error missing when failing to add scratch VHD

Fixes an issue introduced in 298b1378aa39919c4a103c1e450c95bdace16d05.

Signed-off-by: Kevin Parsons <179e5f33d278e7f4e6411489dacfa9a734384f98@microsoft.com>

Microsoft/hcsshim