remove depth from ml_gbt_classification_model and error handle numClasses
remove depth from ml_gbt_classification_model and error handle numClasses

rstudio/sparklyr,kevinykuo/sparklyr,rstudio/sparklyr,rstudio/sparklyr,kevinykuo/sparklyr,rstudio/sparklyr,kevinykuo/sparklyr,kevinykuo/sparklyr