ISPN-2814 RpcManager doesn't return values properly

* Add proper wrapping of ReplicableCommand return values/exceptions into Response objects, to behave exactly as in case of CacheRpcCommands
* Add unit test using some custom commands to prove result wrapping works identically for CacheRpcCommands and ReplicableCommands in general
* CommandAwareRpcDispatcher and InboundInvocationHandlerImpl check if the result is already a Response to avoid double wrapping for legacy commands that do their own wrapping internally
Remove unused class MembershipArithmetic.