loopback: enable diagnostics logging

The loopback example is usually used to debug and develop.
Enable the new diagnostics logging facility, unless -q (quiet)
is passed.

Change-Id: I9ae5214fc33616656832a219fc1470f421786b8c

example/loopback/main.go

@@ -106,6 +106,10 @@ func main() {
 	opts.MountOptions.Name = "loopback"
 	// Leave file permissions on "000" files as-is
 	opts.NullPermissions = true
+	// Enable diagnostics logging
+	if !*quiet {
+		opts.Logger = log.New(os.Stderr, "", 0)
+	}
 	server, err := fs.Mount(flag.Arg(0), loopbackRoot, opts)
 	if err != nil {
 		log.Fatalf("Mount fail: %v\n", err)