Fix sysfs_battery.py hang without battery

If battery is not present, test case should fail instead of sticking

BUG=chrome-os-partner:24928
TEST=manaully test on DUT w/o battery

Change-Id: I2364ef577a0aa9b9200bf83119dd82cf5b2109e2
Reviewed-on: https://chromium-review.googlesource.com/182014
Reviewed-by: Justin Chuang <jchuang@chromium.org>
Commit-Queue: Heng-ruey Hsu <henryhsu@chromium.org>
Tested-by: Heng-ruey Hsu <henryhsu@chromium.org>
1 file changed