[Pyzoo & zoo] Support XGBoost from Python & Add Utest in Pyzoo (#4089)
[Pyzoo & zoo] Support XGBoost from Python & Add Utest in Pyzoo (#4089)

* Support XGBoost in Python

* Remove Redundant

* Remove Redudant, add Engine.init_

* Fix Format

* fix pr validation

* fix xgboost

* fix error

* add Boston Dataset example, add Readme

* fix

* change

* fix

* fix

* Add set Round, num worker function, fix minor issues

* fix minor

* Add test shell, modify README

* fix

* add spark version check
intel-analytics/BigDL,intel-analytics/BigDL,yangw1234/BigDL,yangw1234/BigDL,yangw1234/BigDL,yangw1234/BigDL,intel-analytics/BigDL,intel-analytics/BigDL