Move to_sample_rdd to utils and remove tfnet from pipeline api (#2497)
Move to_sample_rdd to utils and remove tfnet from pipeline api (#2497)

* move to_sample_rdd to utils

* fix test

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