[MRG+1] Return list instead of 3d array for MultiOutputClassifier.predict_proba (#8095)

* Return list instead of 3d array for MultiOutputClassifier.predict_proba

* Update flake8, docstring, variable name

 - Changed `rs` to `rng` to follow convention.
 - Made sure changes were flake8 approved
 - Add `\` to continue docstring for `predict_proba` return value.

* Sub random.choice for np.random.choice

`np.random.choice` isn’t available in Numpy 1.6, so opt for the Python
version instead.

* Make test labels deterministic

* Remove hanging chad...

* Add bug fix and API change to whats new