Fix pylint warnings in update_device.py

We weren't actually using our own pylintrc file in repo upload hook,
which will be fixed by https://android-review.googlesource.com/#/c/platform/tools/repohooks/+/458996/

Even though both camel case and snake case are allowed for function
and method names, they still have to be consistent in a single file.
https://pylint.readthedocs.io/en/latest/user_guide/options.html#multiple-naming-styles

Bug: 27316596
Test: repo upload
Change-Id: I98adba957a547115ef3d8b00fe2e3e4931707b31
(cherry picked from commit 1048559a)
Reviewed-on: https://chromium-review.googlesource.com/848502


Commit-Ready: Amin Hassani <ahassani@chromium.org>
Tested-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Sen Jiang <senj@chromium.org>