Adds Hyper-V soft shutdown implementation

This commit gives the Hyper-V guest VMs a chance to
shutdown gracefully within a time limit, doing a
hard shutdown if they fail to do so.

Partially-Implements: blueprint user-defined-shutdown

Change-Id: I68361ab43d8bba96af063b2ec53f89833a30d02a
Merge "Adds Hyper-V soft shutdown implementation"