Make harness return performance results (#120)
Make harness return performance results (#120)

* Make harness return performance results

As discussed in #109 there is an opportunity to connect OpenTuner
to tune parameters for existing experts.

This change makes test_harness return performance result as a nested
dictionary that contains the same information as what's currently
printed to stdout. As the result, it can be invoked programmatically.

* Address feedback
iree-org/iree-llvm-sandbox,iree-org/iree-llvm-sandbox,iree-org/iree-llvm-sandbox,iree-org/iree-llvm-sandbox