Make TrackerTest random numbers consistent across platforms.

[acolwell]

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• [x] I've followed the contributing guidelines to the best of my understanding
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• [x] I've formatted my code according to Natron's code style
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PR Description

What type of PR is this? (Check one of the boxes below)

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [x] Improvement (non-breaking change which does not add functionality nor fixes a bug but improves Natron in some way)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] My change requires a change to the documentation
  • [ ] I have updated the documentation accordingly

What does this pull request do?

Changed TrackerTests that use random numbers to use a specific random number generator and seed so that the random numbers are guaranteed to be the same no matter what platform you are on. This ensures that we are testing with the same data on all platforms.

The existing code used srand/rand which are not guaranteed to be the same implementation across platforms and it was leading to test failures on Windows that were not occurring on Linux.

Have you tested your changes (if applicable)? If so, how?

Yes. The tests now use the same data and pass on Windows & Linux. I haven't tested on Mac, but it should work.