Support feature with one or more tensors for Sample in python  (#1650)
Support feature with one or more tensors for Sample in python  (#1650)

* feature: JTensor to list of JTensors

* correct typo in creating sequential model for multiple inputs

* add test for multiple inputs
yangw1234/BigDL,yangw1234/BigDL,intel-analytics/BigDL,intel-analytics/BigDL,intel-analytics/BigDL,intel-analytics/BigDL,yangw1234/BigDL,yangw1234/BigDL