Add capability of outputting DxDiag when running pipelines

[joaosaffran]

This patch makes pipelines emit dxdiag information when failing.

[damyanp]

Any reason not to just run this all the time? Seems that we'd want to grab the dxdiag output when we see a test run has failed and so it'd be nice if that was always available with the rest of the results.

[damyanp]

Is there a reason this has to be a separate step?

I'm wondering if you ended up doing this to work around dxdiag running asynchronously, which means that the "DxDiag report saved to $output" message gets printed before the output is actually? In which case this would only happen to work by luck and sometimes you'd not get output at all.

If you run dxdiag like this in powershell:

dxdiag /t $output | Out-Null

Then that command will only complete once the file has been written, and so you can safely assume it is there.

[damyanp]

LGTM, although I wonder if we need to limit this to just failures? If we suspect that a failure may be caused by a driver update then we'd want to compare dxdiag between a successful run and the failing run.