Hyper-V: cleanup basevolumeutils

This patch implements a TODO that was there for some time now,
using Regex in order to retrieve the disk number from a physical
drive path.

Also, some WQL queries have been replaced with filters, which
are cleaner and safer.

Change-Id: I6ee54b72b142cffc271b271937f1b3f9b6b6dbdf
Merge "Hyper-V: cleanup basevolumeutils"