add keras learning phase support (#1065)
add keras learning phase support (#1065)

* add keras learning phase support

* support sessionconfig in python

* fix example

* fix bug

* remove config from api

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