virtualenv_wrapper: convert all users to python3 only

BUG=chromium:997354
TEST=CQ passes

Change-Id: I0f93f61e56aa84efbab0386f1151bebd7f2f4f63
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2063224
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Reviewed-by: Allen Li <ayatane@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/sysmon/osinfo_metrics_unittest.py b/scripts/sysmon/osinfo_metrics_unittest.py
index 52dff4e..bdd5e5d 100644
--- a/scripts/sysmon/osinfo_metrics_unittest.py
+++ b/scripts/sysmon/osinfo_metrics_unittest.py
@@ -10,12 +10,17 @@
 from __future__ import absolute_import
 from __future__ import print_function
 
+import sys
+
 import mock
 
 from chromite.lib import cros_test_lib
 from chromite.scripts.sysmon import osinfo_metrics
 
 
+assert sys.version_info >= (3, 6), 'This module requires Python 3.6+'
+
+
 class TestOSInfoMetrics(cros_test_lib.TestCase):
   """Tests for osinfo_metrics."""