Currently the logic about volume deletion seems to be that an event
should be emitted when the volume delete is requested, not when the
deletion completes.
The VolumeStateListener specifically ignores destroy events for ROOT
volumes, assuming that the ROOT volume only gets deleted when the
instance is destroyed and the UserVmManager should take care of it.
When deleting an account, all of its resources get destroyed, but the
instance expunging circumvents the UserVmManager, and thus we miss the
VOLUME_DESTROY usage event. The account manager now attempts to
propperly destroy the vm before expunging it. This way the destroy
logic is respected, including the event emission.
