Re: [infra-tests][url-tests] Raise stability errors to be visible in PR comments (#4916)

Adding screenshot of flaky test result from this PR for posterity before removing that DEBUG commit:

![raise_errors](https://cloud.githubusercontent.com/assets/94167/23171663/238b8678-f821-11e6-8e86-6937c4f95c95.png)


View on GitHub: https://github.com/w3c/web-platform-tests/pull/4916#issuecomment-281378327

Received on Tuesday, 21 February 2017 15:33:27 UTC