Fixes Hyper-V resize down exception

The Hyper-V driver does not support resize down and is currently
raising an exception if the user attempts to do that, causing the
instance to go in ERROR state.

The driver should use the recently introduced instance faults
"exception.InstanceFaultRollback" instead, which will leave the
instance in ACTIVE state as expected.

Closes-Bug: #1354448

Change-Id: Ibaf8482562094cd2b3165dc62a907fa9e0e56e19

Conflicts:
	nova/virt/hyperv/migrationops.py
Fixes Hyper-V vm state issue

The method which gets VM related information can fail if the
vm is in an intermediary state such as "Shutting down".
The reason is that some of the Hyper-V specific vm states
are not defined as possible states.

This patch assures that a valid state is always returned by
this method.

Change-Id: I64e95f6b537e83a30dd64474f63f140e0e8e7373
Closes-Bug: #1352428