Change the way to import ONNX model. (#186, #187) (#189)

* Change the way to import ONNX model.

* Decide ONNX version and change the processing

* Check whether onnx has the attribute '__version__'

nnvm/tests/python/frontend/onnx/test_graph.py

@@ -5,8 +5,13 @@ from nnvm.compiler import graph_util, graph_attr
 from model_zoo import super_resolution
 
 def compare_graph(onnx_file, nnvm_sym, ishape):
-    onnx_graph = onnx.load(onnx_file)
-    onnx_sym, params = nnvm.frontend.from_onnx(onnx_graph)
+    onnx_vars = [int(n) for n in onnx.__version__.split('.')] if hasattr(onnx, "__version__") else []
+    if len(onnx_vars) >= 2 and (onnx_vars[0] > 0 or onnx_vars[1] >= 2):  # version >= 0.2
+        onnx_model = onnx.load(onnx_file)
+        onnx_sym, params = nnvm.frontend.from_onnx(onnx_model.graph)
+    else:
+        onnx_graph = onnx.load(onnx_file)
+        onnx_sym, params = nnvm.frontend.from_onnx(onnx_graph)
     g1 = nnvm.graph.create(onnx_sym)
     g2 = nnvm.graph.create(nnvm_sym)
     ishapes = {'input_0': ishape}