Changes to MOE defaults

This changes the default MOE endpoint. The difference comes when you have >0 experiments in the PENDING state, and it affects what guesses MOE makes about how those experiments are going to turn on when it recommends the next point. Once I understand the tradeoffs between the methods better, I will add some explanation to the docstrings.

cc: https://github.com/Yelp/MOE/issues/420