Now that I am actually
implementing this I am wondering why don't we simply add
getUUID to CacheRpcCommand. CancellationService will use
this UUID for command cancellation, some other services
might need UUID for something else. Introducing
CancellableCommand does not add much except bunch of
instanceof constructs and explicitly connects UUID with
concept of command cancellation which might not been only
valid use of command UUID.
No, this should be on CancellableCommand only. No sense in
engineering for something we may not need and polluting
interfaces.