Async actions should not try to validate the value according DataSchema

[danielpeintner]

An async action might return an ActionStatus payload instead of the value/type provided in output term

At the moment node-wot throws Error: Invalid value according to DataSchema if the type does not match

relates also somehow to https://github.com/w3c/wot-profile/issues/405 What to do if synchronous is not set which means that no claim on the synchronicity of the action can be made