Errors returned in the publish (grpc) response are ignored

[jcooklin]

If a grpc based plugin returns an error in the publish reply object the framework ignores the error and continues like it was a successful execution of the workflow.

The task given below should eventually go into a disabled state however currently the error is undetected when it's passed back in the reply object.

rand-file.yml
---
  version: 1
  schedule:
    type: "simple"
    interval: "1s"
  workflow:
    collect:
      metrics:
        /random/integer: {}
      publish:
        -
          plugin_name: test-file-publisher
          config:
            file: /tmp/rand-file.out
            return_error: true