glg.go
func FailFunc(f func() string) error {
	if isModeEnable(FAIL) {
		return glg.out(FAIL, "%s", f())
	}
	return nil
}
func FailFunc(f func() string) error {
	if isModeEnable(FAIL) {
		return glg.out(FAIL, "%s", f())
	}
	return nil
}
// FailFunc outputs Fail level log returned from the function