site_utils: Ignore dummy thermal zones.

Ignore IO errors when reading temperature values from dummy thermal
zones.

BUG=chromium:517556
TEST=Manually verify with:
     `test_that --board veyron_jaq --fast chromeos4-row4-rack6-host5.cros \
      graphics_WebGLAquarium`

Change-Id: I3eadb899ae08e9b6e76bac22b0a9a0285b28b118
Signed-off-by: Ricky Liang <jcliang@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/294044
Reviewed-by: Rohit Makasana <rohitbm@chromium.org>
1 file changed