keras input data validation (#3957)
keras input data validation (#3957)

* input validation for keras models

* Modify test for data checking

* Fix errors in input validation

* Minor fix of error message

* Add data checking test

* Add string description to TensorMeta

* Fix code style

* fix test

* fix style

* fix test case

Co-authored-by: Zhenhao Gu <17a6853c19b9d66b136bf015120b954f5d58d945@sjtu.edu.cn>
intel-analytics/BigDL,yangw1234/BigDL,yangw1234/BigDL,intel-analytics/BigDL,yangw1234/BigDL,intel-analytics/BigDL,yangw1234/BigDL,intel-analytics/BigDL