Adds support for Hyper-V image formats

Adds support for VHD and VHDX image formats, including gz compression.

Note: variables naming case changed to match the target branch

(cherry picked from ca8239449fbdbc3a73f691683be2ec9d4a941ff6)

Change-Id: I9b143c9883b947397b435a671f13703f78019d23
Closes-bug: #1353726
Merge "Adds support for Hyper-V image formats" into stable/icehouse