Makes errors from the worker clearer

[bryan-hoang]

Currently, errors from the worker are prefixed with use-dcp-worker: <error from worker>. Some folks have been finding that confusing, thinking that it's a bug with use-dcp-worker rather than with the worker or its configuration.

I think leaving the error reporting to the worker itself instead of trying to wrap the error handling would simplify the issue, leaving control over error handling to application developers.