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: Ic0ddd990c7bb78a020990a9cff01ae2a27f29e1a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2066684
Reviewed-by: Alex Klein <saklein@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/cros_run_unit_tests_unittest.py b/scripts/cros_run_unit_tests_unittest.py
index 8e13669..4dffadb 100644
--- a/scripts/cros_run_unit_tests_unittest.py
+++ b/scripts/cros_run_unit_tests_unittest.py
@@ -7,10 +7,15 @@
 
 from __future__ import print_function
 
+import sys
+
 from chromite.lib import cros_test_lib
 from chromite.scripts import cros_run_unit_tests
 
 
+assert sys.version_info >= (3, 6), 'This module requires Python 3.6+'
+
+
 class DetermineBoardPackagesTest(cros_test_lib.TestCase):
   """Tests that package determination returns a non-empty set"""