Clean up Lint warnings in write_firmware.py and host/cros_bundle_firmware

Presubmit hooks reported many lint violations in host/lib/write_firmware.py.
Fixing them required a change in host/cros_bundle_firmware as well (mutable
objects used as default parameters are dangerous).

BUG=None
TEST=manual

  . observed the following command succeed after connecting the A-A cable
    between the DUT and the host

    cros_write_firmware -b daisy -w usb -d exynos5250-snow -F spi -i \
           /build/daisy/firmware/image-snow.bin -V

Change-Id: I9fc50d155d83c8edab846df61cc2b7b46ef86be6
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/42012
Reviewed-by: Simon Glass <sjg@chromium.org>
2 files changed