Adds ephemeral storage support for Hyper-V

Blueprint: hyper-v-ephemeral-storage

This patchset adds support for creating an ephemeral storage dynamic
VHD or VHDX (based on the versions of vhdutils used) when an instance is
spawned.

The ephemeral disk is correctly migrated during migration/resize and
live migration.

The ephemeral virtual disk is not partitioned or formatted, leaving the
task to guest side tools (e.g.: cloud-init or cloudbase-init).

Change-Id: I0b5d6b55ccdc981efcd507c45184fb2d528bf9c1
Merge "Adds ephemeral storage support for Hyper-V"