Format output of docker info

Format those info which will only be displayed when daemon is
in debug mode.

Signed-off-by: Hu Keping <hukeping@huawei.com>

pkg/ioutils/fmt.go

@@ -12,3 +12,11 @@ func FprintfIfNotEmpty(w io.Writer, format, value string) (int, error) {
 	}
 	return 0, nil
 }
+
+// FprintfIfTrue prints the boolean value if it's true
+func FprintfIfTrue(w io.Writer, format string, ok bool) (int, error) {
+	if ok {
+		return fmt.Fprintf(w, format, ok)
+	}
+	return 0, nil
+}