Fix the ONNX parser tests issues due to a change in the latest ONNx master

Fix the ONNX parser tests issues due to a change in the latest ONNx master

 * A recent change in ONNX now forces the data types to be indicated by the
   integer corresponding to their original enum value
 * The new values are taken from the TensorProto_DataType enum at onnx.pb.h:153

Change-Id: I6054611795a7edb11463396eaefc4dd7e27261a0