Perf dashboard erroneously shows an old OS build in A/B testing range

Perf dashboard erroneously shows an old OS build in A/B testing range
https://bugs.webkit.org/show_bug.cgi?id=149942

Reviewed by Darin Adler.

Ordering OS builds lexicologically turned out be a bad idea since 15A25 falls between 15A242 and 15A251.
Use a fake/synthetic timestamp to force the commonly understood total order instead.

Refactored pull-os-versions.py to share the server config JSON with other scripts. Also made the script
support pulling multiple sources; e.g. both OS X and iOS.

Also removed superfluous feature to submit results in chunks. The perf dashboard can handle thousands of
revisions being submitted at once just fine.

* public/api/commits.php:
(main): A partial revert of r185574 since we no longer need to order builds lexicologically.

* tools/pull-os-versions.py:
(main): Takes --os-config-json, --server-config-json, and --seconds-to-sleep as arguments instead of
a single --config argument to share the server config JSON with other scripts.
(OSBuildFetcher): Extracted out of main. This class is instantiated for each OS kind (e.g. OS X).
(OSBuildFetcher.__init__): Added.
(OSBuildFetcher._fetch_available_builds): Extracted out of main. Fetches available builds from a website
or custom commands.
(OSBuildFetcher.fetch_and_report_new_builds): Extracted out of main. Submits the fetched builds after
filtering out the ones we've already reported.
(OSBuildFetcher._assign_fake_timestamps): Creates a fake timestamp to establish a total order amongst each
OS X / iOS style build number such as 12A3456b.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@190817 268f45cc-cd09-0410-ab3c-d52691b4dbfc