Add an API to get node from graph model with given name (#1871)
Add an API to get node from graph model with given name (#1871)

* get node from graph

* add unit test

* add Graph.node api in python

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