actually honor provided stdin/stdout

the BackupTar and RestoreTar functionality was ignoring provided
readers, which doesn't matter for real usage but breaks tests
by making them dump raw tar binaries to stdout.

(cherry picked from commit 93153a97db)

ctl/backup_tar.go

@@ -127,7 +127,7 @@ func (cmd *BackupTarCommand) Run(ctx context.Context) (err error) {
 	// Create output file in temporary location, or send to stdout if a dash is specified.
 	var w io.Writer
 	if useStdout {
-		w = os.Stdout
+		w = cmd.Stdout
 	} else {
 		f, err := os.Create(cmd.OutputPath + ".tmp")
 		if err != nil {

ctl/restore_tar.go

@@ -73,16 +73,17 @@ func (cmd *RestoreTarCommand) Run(ctx context.Context) (err error) {
 	}
 	useStdin := cmd.Path == "-"
 
-	var f *os.File
+	var f io.Reader
 	// read from Stdin if path specified as -
 	if useStdin {
-		f = os.Stdin
+		f = cmd.Stdin
 	} else {
-		f, err = os.Open(cmd.Path)
+		file, err := os.Open(cmd.Path)
 		if err != nil {
 			return (err)
 		}
-		defer f.Close()
+		defer file.Close()
+		f = file
 	}
 
 	// Parse TLS configuration for node-specific clients.