support spark dataframe in tf2 estimator (#3113)
support spark dataframe in tf2 estimator (#3113)

* support spark dataframe in tf2 estimator

* fix style
yangw1234/BigDL,intel-analytics/BigDL,yangw1234/BigDL,intel-analytics/BigDL,yangw1234/BigDL,yangw1234/BigDL,intel-analytics/BigDL,intel-analytics/BigDL