Fix optimizer state messed up when calling optimize() multiple times in DistriOptimizer (#2178)
Fix optimizer state messed up when calling optimize() multiple times in DistriOptimizer (#2178)

* support continue training

* meet code review

* add unit tests

* fix set model

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