Major Description
Several cleanup and improvements for spark.logit:
- summary should return coefficients matrix, and should output labels for each class if the model is multinomial logistic regression model.
- summary should not return areaUnderROC, roc, pr, ..., since most of them are DataFrame which are less important for R users. Meanwhile, these metrics ignore instance weights (setting all to 1.0) which will be changed in later Spark version. In case it will introduce breaking changes, we do not expose them currently.
- SparkR test improvement: comparing the training result with native R glmnet.
- Remove argument aggregationDepth from spark.logit, since it's an expert Param(related with Spark architecture and job execution) that would be used rarely by R users.
