Automatic merge from submit-queue (batch tested with PRs 55016, 50887). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
If command.Execute() return err, print to stdErr
The current kube-proxy not print error if (execute() failed) . not so good and not so friendly to user.
If print err to stdError, will show us why it failed.
9c41f9baf1