rspec: Websockets Sample returns HTML failed

Note: #1566 was also for this test, but it was closed more than 10 days ago. So, I didn't mark it flaky. ---- commit: 20cbd73e641cf0e16e89d1ddfea31d96210b1bbb buildURL: [Build Status](https://source.cloud.google.com/results/invocations/edcaf68e-2d8f-4b2b-ab30-2daf917c8000), [Sponge](http://sponge2/edcaf68e-2d8f-4b2b-ab30-2daf917c8000) status: failed