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_install_debug_syms.py b/scripts/cros_install_debug_syms.py
index d4f0bc1..710475b 100644
--- a/scripts/cros_install_debug_syms.py
+++ b/scripts/cros_install_debug_syms.py
@@ -20,6 +20,7 @@
 import multiprocessing
 import os
 import pickle
+import sys
 import tempfile
 
 from six.moves import urllib
@@ -39,6 +40,10 @@
   # pylint: disable=import-error
   from portage import create_trees
 
+
+assert sys.version_info >= (3, 6), 'This module requires Python 3.6+'
+
+
 DEBUG_SYMS_EXT = '.debug.tbz2'
 
 # We cache the package indexes. When the format of what we store changes,