Fix creating sc when import bigdl.nn.keras and check version (#543)
Fix creating sc when import bigdl.nn.keras and check version (#543)

* fix

* fix

* fix check version

* fix ut

* fix example

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