Cleaning up and refactoring gms update/preprocess scripts

Also, add a pylib.utils.argpars_utils.CustomHelpAction
to support multiple help commands

Changelog for the android_tools roll:
https://chromium.googlesource.com/android_tools/+/54492f99c84cab0826a8e656efeb33a1b1bf5a04..f4c36ad89b2696b37d9cd7ca7d984b691888b188

BUG=541727

Review URL: https://codereview.chromium.org/1469913002

Cr-Commit-Position: refs/heads/master@{#365548}
11 files changed