Fixes cinder volume create on Windows Server 2012 R2

Windows Server 2012 R2 does not support vhd images as iSCSI disks,
requiring VHDX images. For this reason, the cinder driver fails to
create volumes. For the moment, the default format is vhd.
On WSS 2012 R2, we should use vhdx images as default.

This patch introduces vhd/vhdx related methods for both v1 and v2
wmi virtualization namespaces.

Closes-Bug: #1299150
Change-Id: I272988dc5b0e3b8129c5e4d3c79bea1c292701c8
Merge "Fixes cinder volume create on Windows Server 2012 R2"