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_choose_profile.py b/scripts/cros_choose_profile.py
index 02ff9f9..4cf03af 100644
--- a/scripts/cros_choose_profile.py
+++ b/scripts/cros_choose_profile.py
@@ -9,6 +9,7 @@
 
 import functools
 import os
+import sys
 
 import six
 
@@ -19,6 +20,9 @@
 from chromite.lib import sysroot_lib
 
 
+assert sys.version_info >= (3, 6), 'This module requires Python 3.6+'
+
+
 # Default value constants.
 _DEFAULT_PROFILE = 'base'