WFLY-3519 process-id-uuid and related attribute should consider alternat...

...ives/required attributes in :write-attribute handler
This looks good, but please encapsulate it in an anonymous OperationStepHandler and have validateUpdatedModel call context.addStep(theStep, Stage.MODEL). That way if the user provides a composite op, all the steps in the op will execute before this validation happens, allowing, for example, the 1st step to set PROCESS_ID_UUID to false, and the 2nd step to set PROCESS_ID_SOCKET_BINDING to some value.

A test in the subsystem test to validate that works would be good.