fn: enable failing test back (#826)

* fn: enable failing test back

* fn: fortifying the stderr output

Modified limitWriter to discard excess data instead
of returning error, this is to allow stderr/stdout
pipes flowing to avoid head-of-line blocking or
data corruption in container stdout/stderr output stream.

api/agent/drivers/docker/docker.go

@@ -145,6 +145,8 @@ func (drv *DockerDriver) Prepare(ctx context.Context, task drivers.ContainerTask
 			Image:        task.Image(),
 			Volumes:      map[string]struct{}{},
 			OpenStdin:    true,
+			AttachStdout: true,
+			AttachStderr: true,
 			AttachStdin:  true,
 			StdinOnce:    true,
 		},