Fix perf dashboard tests for node v8

Fix perf dashboard tests for node v8
https://bugs.webkit.org/show_bug.cgi?id=181782

Reviewed by Wenson Hsieh.

Fixed the various tests for node.js v8, which is the latest LTS version.

* server-tests/api-manifest-tests.js: Replaced the missing Triggerable.acceptsTest by Triggerable.acceptedTests
after r226836.
* server-tests/api-measurement-set-tests.js: Added "Z" to the end timestamps to force UTF timezone now that Date
in node.js parses using the local timezone by default.
* server-tests/resources/test-server.js:
(TestServer.prototype._restoreDataDirectory): Fixed the bug that this function was erroneously using the async
function to rename a directory per new warnings. This code was racy, and it used to cause a test error occasionally.
* server-tests/tools-os-build-fetcher-tests.js: Fixed the assertions to make it work in the latest node.js.
* unit-tests/measurement-set-tests.js:
(waitForMeasurementSet): Wait for setTimeout to cycle through all microtasks instead of just two microtask cycles.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@227122 268f45cc-cd09-0410-ab3c-d52691b4dbfc