Build: Improve Saucelabs testing

Switch from the Mocha reporter to the custom one that handles mocha better ...
Still encountering random errors, but pass rate is higher using the JS API.
- Changed concurrency to the new throttled option
- Bumped Expect.js, which also removes a package.json warning
- Bump Mocha to latest
- Bump Sinon to latest
Merge pull request #5284 from nschonni/saucelabs-5

Build: Improve Saucelabs testing