Add support for test262 JavaScriptCore tests

Add support for test262 JavaScriptCore tests
https://bugs.webkit.org/show_bug.cgi?id=170523

Reviewed by Daniel Bates.

* BuildSlaveSupport/build.webkit.org-config/config.json: Added bot433 and bot434.
* BuildSlaveSupport/build.webkit.org-config/master.cfg:
(RunTest262Tests): Added class to run Test262 tests.
(RunTest262Tests.start): Added.
(RunTest262Tests.countFailures): Method to count the failures.
(Test262Factory): Added Test262 factory class.
* BuildSlaveSupport/build.webkit.org-config/mastercfg_unittest.py:
(RunTest262TestsTest): Added unit tests.
(RunTest262TestsTest.assertResults): Helper method.
(RunTest262TestsTest.test_no_regressions_output): Added test case.
(test_failure_output): Same.
(test_failures_output): Same.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@215108 268f45cc-cd09-0410-ab3c-d52691b4dbfc