convert a few dev scripts to wrapper3

These tools are mostly run by devs.  Cut them over to get feedback.

BUG=chromium:997354
TEST=`./run_tests` passes

Change-Id: I36568b56f852a24224b8c2f05cfa34fdf1062d5c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2048209
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/gerrit.py b/scripts/gerrit.py
index 734a84f..37c3a41 100644
--- a/scripts/gerrit.py
+++ b/scripts/gerrit.py
@@ -31,6 +31,9 @@
 from chromite.utils import memoize
 
 
+assert sys.version_info >= (3, 6), 'This module requires Python 3.6+'
+
+
 # Locate actions that are exposed to the user.  All functions that start
 # with "UserAct" are fair game.
 ACTION_PREFIX = 'UserAct'