Fixes Hyper-V volume mapping issue on reboot

Hyper-V does not manage iSCSI mounted passthrough disks
correctly on reboot in some circumstances where disk
number assignment can change, resulting in instances potentially
booting with the wrong volume attached.

Co-Authored-By: Adelina Tuvenie <atuvenie@cloudbasesolutions.com>
Co-Authored-By: Adrian Bora <abora@cloudbasesolutions.com>

Closes-Bug: #1322926
(cherry picked from commit 50636a881b60f112027494bcd84af66888db8c1c)

Conflicts:
	nova/tests/virt/hyperv/test_vmutils.py
	nova/tests/virt/hyperv/test_vmutilsv2.py
	nova/virt/hyperv/vmutils.py
	nova/virt/hyperv/vmutilsv2.py

Change-Id: I99fa75aaa950de2ada8a03bd23c910c3ff810d69
Merge "Fixes Hyper-V volume mapping issue on reboot" into stable/icehouse