Distance in KMeansMachine is square Euclidean

Created by: laurentes

Preparing the Bob tutorial, I've just noticed that the distance returned by the getDistanceFromMean() method of the KMeansMachine class is not the Euclidean distance, but the square Euclidean distance. This is not a real problem because of the bijection between these two, but to my mind, this needs to be updated. For this purpose, we need to update/add tests, and make sure that it does not affect our baseline results.