image: Convert cros_set_lsb_release to python

BUG=brillo:1010
TEST=manual; built image before and after change, compared
     the lsb-release files of each
CQ-DEPEND=CL:272517

Change-Id: I2430fa44f4427793c4555bcf32ac07d5495195e4
Reviewed-on: https://chromium-review.googlesource.com/272547
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Sheng-liang Song <ssl@chromium.org>
Commit-Queue: Steve Fung <stevefung@chromium.org>
Trybot-Ready: Steve Fung <stevefung@chromium.org>
Tested-by: Steve Fung <stevefung@chromium.org>
1 file changed