Upload xunit performance results to benchview - #4

@john-soklaski This looks great, thanks!

Just three small things before merging:

• Could you trim trailing spaces in the file?
• I think it would look better if we split the calls to all of the benchview tools into multi-line argument lists, like you did for submission.py and upload.py.
• Could you squash this down before the merge to avoid the duplicate payload for PR Acqure benchview tools using nuget #2?

@dpodder Thanks for the feedback. I've addressed all three points