Set coordinate_transformation_mode=asymmetric when rewriting Upsample to Reshape to get same output.

[jorickert]

Edit: Need to investigate why onnx-runtime and the backend tests have different results

Before the rewrite would rewrite to an reshape with the default coordinate_transformation_mode = "half_pixel", but this leads to a different output when comparing with onnx runtime.
Tested using onnx runtime, with one model having a Reshape Op and one an Upsample. With coordinate_transformation_mode = "half_pixel" the output had some differences, with coordinate_transformation_mode = "asymmetric" the output was the same.
Comment in ORT about this: microsoft/onnxruntime#1179 (comment)

IMO the onnx documentation for Upsample is not very detailed and its hard to know how to do the Upsample -> Reshape rewrite when just looking at the documentation.