Add get sample method for ImageFrame (#2447)
Add get sample method for ImageFrame (#2447)

* add get sample method

* add test

* fix style

* fix style

* fix style

* fix style

* fix test case

* fix test case

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