add mmdebstrap prefix to temporary directory name

mmdebstrap

@@ -1873,7 +1873,10 @@ sub main() {
     if ($options->{maketar}) {
 	# since the output is a tarball, we create the rootfs in a temporary
 	# directory
-	$options->{root} = tempdir();
+	$options->{root} = tempdir(
+	    'mmdebstrap.XXXXXXXXXX',
+	    DIR => File::Spec->tmpdir
+	);
 	# in unshare and root mode, other users than the current user need to
 	# access the rootfs, most prominently, the _apt user. Thus, make the
 	# temporary directory world readable.