An error messages must write to standard error.

[qt-luigi]

Describe the proposal

In present, An error messages write to standard output (os.Stdout).

print.FailureStatusEvent(os.Stdout, err.Error())
print.FailureStatusEvent(os.Stdout, "an error message")

These must write to standard error (os.Stderr).

print.FailureStatusEvent(os.Stderr, err.Error())
print.FailureStatusEvent(os.Stderr, "an error message")

Release Note

RELEASE NOTE:

[daixiang0]

/assign