usb_updater: Migrate fw_update.py to python2/3 compatible
usb_updater: Migrate fw_update.py to python2/3 compatible

BUG=chromium:1031705
BRANCH=master
TEST=None

Signed-off-by: kerker <b60348db21a0b73e8345c1da67719faa1d4da16e@chromium.org>
Change-Id: I00a1c0868980e9b8a03ad13ea000fbe94ef3192f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2425791
Reviewed-by: Hung-Te Lin <8a7fce4940baad93a69f5073b383c85deed9d9c4@chromium.org>
Reviewed-by: Jack Rosenthal <d3f605bef1867f59845d4ce6e4f83b8dc9e4e0ae@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec