Only generate a dashboard for test runs that run to completion.

If a run errors out early, we may not generate a failing_results.json
and the dashboard generator will get confused.

TBR=behara.ms@samsung.com
BUG=

Review URL: https://codereview.chromium.org/585983003

git-svn-id: svn://svn.chromium.org/blink/trunk@182351 bbb929c8-8fbe-4397-9dbb-9b2b20218538