fix error messaging in wrappedmain. Stderr gets eaten by panicwrap, so we need to write to stdout, which then gets unpacked into error and output messages using the ErrorPrefix and OutputPrefix (#10766)

main.go

@@ -152,7 +152,7 @@ func wrappedMain() int {
 	// passed into commands like `packer build`
 	config, err := loadConfig()
 	if err != nil {
-		fmt.Fprintf(os.Stderr, "Error loading configuration: \n\n%s\n", err)
+		fmt.Fprintf(os.Stdout, "%s Error loading configuration: \n\n%s\n", ErrorPrefix, err)
 		return 1
 	}
 
@@ -166,7 +166,7 @@ func wrappedMain() int {
 
 	cacheDir, err := packersdk.CachePath()
 	if err != nil {
-		fmt.Fprintf(os.Stderr, "Error preparing cache directory: \n\n%s\n", err)
+		fmt.Fprintf(os.Stdout, "%s Error preparing cache directory: \n\n%s\n", ErrorPrefix, err)
 		return 1
 	}
 	log.Printf("[INFO] Setting cache directory: %s", cacheDir)
@@ -187,7 +187,7 @@ func wrappedMain() int {
 		// Set this so that we don't get colored output in our machine-
 		// readable UI.
 		if err := os.Setenv("PACKER_NO_COLOR", "1"); err != nil {
-			fmt.Fprintf(os.Stderr, "Packer failed to initialize UI: %s\n", err)
+			fmt.Fprintf(os.Stdout, "%s Packer failed to initialize UI: %s\n", ErrorPrefix, err)
 			return 1
 		}
 	} else {
@@ -202,13 +202,13 @@ func wrappedMain() int {
 			currentPID := os.Getpid()
 			backgrounded, err := checkProcess(currentPID)
 			if err != nil {
-				fmt.Fprintf(os.Stderr, "cannot determine if process is in "+
-					"background: %s\n", err)
+				fmt.Fprintf(os.Stdout, "%s cannot determine if process is in "+
+					"background: %s\n", ErrorPrefix, err)
 			}
 			if backgrounded {
-				fmt.Fprint(os.Stderr, "Running in background, not using a TTY\n")
+				fmt.Fprintf(os.Stdout, "%s Running in background, not using a TTY\n", ErrorPrefix)
 			} else if TTY, err := openTTY(); err != nil {
-				fmt.Fprintf(os.Stderr, "No tty available: %s\n", err)
+				fmt.Fprintf(os.Stdout, "%s No tty available: %s\n", ErrorPrefix, err)
 			} else {
 				basicUi.TTY = TTY
 				basicUi.PB = &packer.UiProgressBar{}
@@ -246,7 +246,7 @@ func wrappedMain() int {
 	}
 
 	if err != nil {
-		fmt.Fprintf(os.Stderr, "Error executing CLI: %s\n", err)
+		fmt.Fprintf(os.Stdout, "%s Error executing CLI: %s\n", ErrorPrefix, err)
 		return 1
 	}