[autotest] Handle json file parsing error

perf_dashboard_shadow_config.json is deployed by puppet and there is no cq to
validate that change. Handle the ValueError in case the json file is
malformated.

BUG=chromium:581382
TEST=None

Change-Id: I91fcfd51b73c5e9654f412ff3c0f630371bd5b30
Reviewed-on: https://chromium-review.googlesource.com/324101
Commit-Ready: Dan Shi <dshi@google.com>
Tested-by: Dan Shi <dshi@chromium.org>
Reviewed-by: Kevin Cheng <kevcheng@chromium.org>
1 file changed