Disable HTTP/2 Alternative Services.

* Temporarily disable HTTP/2 Alternative Services,
  see https://crbug.com/706974#c5 for motivation.
* Rename test-only enable_http2_alternative_service_with_different_host
  to enable_http2_alternative_service and change function accordingly.

BUG=706974

Review-Url: https://codereview.chromium.org/2821463002
Cr-Commit-Position: refs/heads/master@{#464916}
7 files changed