scripts: convert random standalone programs to python3 only

Nothing imports these, so should be safe to convert.

BUG=chromium:997354
TEST=CQ passes

Change-Id: Iced71210aca4ef7e83235b5d8a2959da0193646e
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2071695
Reviewed-by: Alex Klein <saklein@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/test_image_unittest.py b/scripts/test_image_unittest.py
index 5f71285..2379ade 100644
--- a/scripts/test_image_unittest.py
+++ b/scripts/test_image_unittest.py
@@ -8,6 +8,7 @@
 from __future__ import print_function
 
 import os
+import sys
 import tempfile
 import unittest
 
@@ -19,6 +20,9 @@
 from chromite.scripts import test_image
 
 
+assert sys.version_info >= (3, 6), 'This module requires Python 3.6+'
+
+
 class TestImageTest(cros_test_lib.MockTempDirTestCase):
   """Common class for tests ImageTest.