dev: Add coverage variation to deal with flakiness - #335

Mihai, I'm not familiar with codecov, but looking at the docs it says "threshold: allowed to drop X% and still result in a "success"".
So by adding threshold 1, are you allowing 1% test failures to still be a success?
You mention occasional multiprocess test flakiness do to some randomness, do you use the @flaky decorator?

Thanks for having a look at this PR, @gdoubleyew.

Codecov is not looking at directly at test results. In fact, it only runs if the tests were successful. So the threshold only allows the test coverage to drop, it does not allow tests to fail.

The flakiness does not cause test failures in BrainIAK, as far as I can tell. Therefore, we do not need the @flaky decorator to pass tests. Instead, the flakiness causes the coverage to vary. Using @flaky with min_passes > 1 will decrease the chance of a drop in coverage. However, even with a high min_passes, there is still a chance that coverage appears to drop, so we would still see spurious failures. Therefore, I think it is best to introduce the threshold.