Test methods should use parameter checkpoint with best return

[jkterry1]

Right now, test is applied to the parameters at the end of training. Sometimes, this can be much worse than the peak, which is what you'd use any benchmark anyways. Ideally test would automatically do this for you.

[cpnota]

This is the "deep mind" style testing. I've been thinking about the best way to handle this, there's a few options. I'm still not happy with the experiments package as a whole, so may roll this into future refactoring.

If you need this urgently, you should be able to implement a version using between experiment.train(), experiment.test() and experiment.save() by writing your own version of run_experiment