CLOUDSTACK-6833 [Hyper-V] Volume snapshot creation returns success even though snapshots are not supported for Hyper-V

(cherry picked from commit 945e879bf221454cd42f1e7ef0a46e9a4aa6a156)
CLOUDSTACK-6831 [Hyper-V] Improve the logging for VM snapshot failures as it is not supported. Right now it is throwing NPEs

(cherry picked from commit d59cc1ff8fa909d37609410e19142b158cecb2f3)