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: I00c4979de8f4e4f07f793947ab62a8455c253104
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2081374
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/cros_generate_update_payload_unittest.py b/scripts/cros_generate_update_payload_unittest.py
index 5d732c7..529e51f 100644
--- a/scripts/cros_generate_update_payload_unittest.py
+++ b/scripts/cros_generate_update_payload_unittest.py
@@ -7,6 +7,8 @@
 
 from __future__ import print_function
 
+import sys
+
 from chromite.lib import cros_test_lib
 from chromite.lib import partial_mock
 
@@ -16,6 +18,9 @@
 from chromite.scripts import cros_generate_update_payload
 
 
+assert sys.version_info >= (3, 6), 'This module requires Python 3.6+'
+
+
 class CrOSGenerateUpdatePayloadTest(cros_test_lib.MockTestCase):
   """Test correct arguments passed to delta_generator."""