Update python benchmarking script (#4164)
Update python benchmarking script (#4164)

* a few tweaks to speed up data generation

* del variable to save memory

* switch to random numpy arrays

dmlc/xgboost,dmlc/xgboost,dmlc/xgboost,dmlc/xgboost,dmlc/xgboost,dmlc/xgboost