Persist a VZGenericMachineIdentifier in Linux VM configurations and
reuse it when building VZGenericPlatformConfiguration. Saved machine
state is tied to this identifier, so generating a new one prevents
restoration.
Legacy configurations remain loadable but cannot be suspended.
When cloning a stopped legacy Linux VM, initialize the missing identifier
in the clone. Existing identifiers and suspended state remain unchanged.
Linux now conforms to PlatformSuspendable and retains USB keyboard
support in suspendable mode, but omits
VZUSBScreenCoordinatePointingDeviceConfiguration because it passes
save/restore validation but causes restoration to fail.
Randolph Voorhies
Nikolay Edigaryev