depot_tools: Replace pylint error numbers with symbolic names.

This affects a bunch of files, but only changes comments,
and shouldn't make any difference to behavior.

The purpose is to slightly improve readability of pylint
disable comments.

Change-Id: Ic6cd0f8de792b31d91c6125f6da2616450b30f11
Reviewed-on: https://chromium-review.googlesource.com/420412
Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: Quinten Yearsley <qyearsley@chromium.org>
diff --git a/git_cache.py b/git_cache.py
index d4c35df..bae45e7 100755
--- a/git_cache.py
+++ b/git_cache.py
@@ -29,7 +29,7 @@
 GIT_CACHE_CORRUPT_MESSAGE = 'WARNING: The Git cache is corrupt.'
 
 try:
-  # pylint: disable=E0602
+  # pylint: disable=undefined-variable
   WinErr = WindowsError
 except NameError:
   class WinErr(Exception):