Don't return rpc.Status as an explicit response data item

[avive]

All rpc api method calls started by clients return a status code and optional message.
I think that adding a status explicitly in responses is redundant and def not idiomatic grpc pattern.
e.g.:

message StopSmeshingResponse {   
   google.rpc.Status status = 1;
}

There are several other responses such as this in the smesher service.

So a method that just returns a status in its response should use the build-in status and status code.
See: https://grpc.io/docs/guides/error/

So a method that completes without an error and has not data to return such as StopSmeshingResponse should return status == 0 when there's no error or otherwise return one of the pre-defined error statuses and a message as defined here: https://grpc.github.io/grpc/core/md_doc_statuscodes.html - or an un-reserved code with message when one of the reserved error codes is not applicable.

@lrettig - please review.

So, StopSmeshingResponse should be defined like this:

message StopSmeshingResponse {   

}

The following status codes are never generated by the library and can be used:

• INVALID_ARGUMENT
• NOT_FOUND
• ALREADY_EXISTS
• FAILED_PRECONDITION
• ABORTED
• OUT_OF_RANGE
• DATA_LOSS

[lrettig]

I think you're probably right and I think we should probably do this 👍

[avive]

I've implemented this in the 0.3 branch