build-requests should use conform to JSON API format

build-requests should use conform to JSON API format
https://bugs.webkit.org/show_bug.cgi?id=146375

Reviewed by Stephanie Lewis.

Instead of returning single dictionary that maps root set id to a dictionary of repository names
to revisions, timestamps, simply return root sets and roots "rows" or "objects" as defined in
JSON API (http://jsonapi.org/). This API change makes it easier to resolve the bug 146374 and
matches what we do in /api/test-groups.

Also add the support for /api/build-requests/?id=<id> to fetch the build request with <id>.
This is useful for debugging purposes.

* public/api/build-requests.php:
(main): Added the support for $_GET['id']. Also return "rootSets" and "roots".
(update_builds): Extracted from main.

* public/include/build-requests-fetcher.php:
(BuildRequestFetcher::fetch_request): Added. Used for /api/build-requests/?id=<id>.
(BuildRequestFetcher::results_internal): Always call fetch_roots_for_set_if_needed.
(BuildRequestFetcher::fetch_roots_for_set_if_needed): Renamed from fetch_roots_for_set.
Moved the logic to exit early when the root set had already been fetched here.

* public/v2/analysis.js:
(App.TestGroup._fetchTestResults): Fixed the bug that test groups without any successful results
won't be shown.

* tools/pull-os-versions.py:
(main):
(setup_auth): Moved to util.py

* tools/sync-with-buildbot.py:
(main): Replaced a bunch of perf dashboard related options by --server-config-json.
(update_and_fetch_build_requests): No longer takes build_request_auth since that's now taken care
of by setup_auth.
(organize_root_sets_by_id_and_repository_names): Added. Builds the old rootsSets directory based
on "roots" and "rootSets" dictionaries returned by /api/build-requests.
(config_for_request): Fixed a bug that the script blows up when the build request is missing
the repository specified in the configuration. This tolerance is necessary when a new repository
dependency is added but we want to run A/B tests for old builds without the dependency.
(fetch_json): No longer takes auth.

* tools/util.py:
(setup_auth): Moved from pull-os-versions.py to be shared with sync-with-buildbot.py.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@186033 268f45cc-cd09-0410-ab3c-d52691b4dbfc