[Stopwatch] Fix tests on Travis (also vagrant)

Travis often fails to run tests related to the Stopwatch Component, check it yourself:

- https://travis-ci.org/symfony/symfony/jobs/12340378
- https://travis-ci.org/symfony/symfony/jobs/12365787
- https://travis-ci.org/symfony/symfony/jobs/12365790
- https://travis-ci.org/symfony/symfony/jobs/12367771
- https://travis-ci.org/symfony/symfony/jobs/12367844
- https://travis-ci.org/symfony/symfony/jobs/12368619
- https://travis-ci.org/symfony/symfony/jobs/12371316
- https://travis-ci.org/symfony/symfony/jobs/12375730

This is because Travis is just slow as hell. So I just multiply the used usleep by 10.