Benchmark version changes should be possible through the wrapper

[frival]

The way the wrapper is written now, if there's a PerformanceTest directory it will always use that regardless of whether it matches the contents of the uploaded zip file. The intention is good - if the user has made intentional changes we should honor them and not blindly overwrite them - but the result is that upgrading a version of the benchmark requires manual intervention on the target host and that the user knows where the benchmark winds up running (in this case in the benchmark user's $HOME). I propose we offer a --upgrade option (or another, similar name) that will either move aside the PerformanceTest directory or remove it and replace its contents by extracting the new archive.