util: Migrate inject-keys.py to python2/3 compatible
util: Migrate inject-keys.py to python2/3 compatible

BUG=chromium:1031705
BRANCH=master
TEST=`test-inject-keys.sh` pass with python2, python3 shebang

Signed-off-by: kerker <b60348db21a0b73e8345c1da67719faa1d4da16e@chromium.org>
Change-Id: I61e7fe8525f8b836dae5eedd74f090899ac019e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2422111
Reviewed-by: Yu-Ping Wu <e17b963d2ce5bddd1fecae25c320252b132e804d@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