site_utils: Get temperature from thermal_zones.

Search /sys/class/thermal/thermal_zones*/temp when looking for the
maximum temperature readings on the system.

BUG=chrome-os-partner:43302 chromium:517556
TEST=Run `test_that --board <board> --fast <remote> graphics_WebGLAquarium`
     and verify the test passes without error.

Change-Id: Ia7c0d204091cae69a889f7215e3f204647b03aac
Signed-off-by: Ricky Liang <jcliang@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/293050
Reviewed-by: Rohit Makasana <rohitbm@chromium.org>
1 file changed