onnxruntime

Add a couple of utility scripts to tools/python (#3621)

* Add a helper script to more easily create a test directory for use with onnx_test_runner or onnxruntime_perf_test.
Add example script that can be used as a base for performance testing a model with a variety of input sizes.
Add __init__.py so files in this directory can be imported in other scripts.

* Fix some flake8 warnings.
Add example of specifying attribute for op.

* Add ability for test dir creation to fill in all missing input data with random values.
Add example of using test dir creation this way