Fixes Hyper-V boot from volume root device issue

Checks that instances are booting from volume by checking
the correct root device obtained from the block device info.

Change-Id: I94941dfe96c1596c8e9b91df3d3d19d33ae7fe92
Co-Authored-By: Zsolt Dudas <zdudas@cloudbasesolutions.com>
Closes-Bug: #1357972
Merge "Fixes Hyper-V boot from volume root device issue"