Avoid "KeyError: 'exit_code'" error in failed shard detection Apparently there are cases where a shard is broken but exit_code is not present in json. Example build: https://ci.chromium.org/ui/p/angle/builders/ci/android-pixel4-perf/4038/overview Bug: chromium:1346781 Change-Id: I7ee5b8cac5da3123e5b57b3bca393db12ce8921a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4414233 Commit-Queue: Roman Lavrov <romanl@google.com> Reviewed-by: Amirali Abdolrashidi <abdolrashidi@google.com>