[new feature] multi optimMethods support in Optimizer (#2560)
[new feature] multi optimMethods support in Optimizer (#2560)

* multiOptimMethod

* some update

* fix unit test

* fix ut

* fix unit test

* fix python unit test

* meet code review

* update optimizer.py

* update python

* meet code review

intel-analytics/BigDL,intel-analytics/BigDL,yangw1234/BigDL,yangw1234/BigDL,yangw1234/BigDL,intel-analytics/BigDL,intel-analytics/BigDL,yangw1234/BigDL