CI: Some Azure Pipelines cleanups
Hey all, I'm a PM on Azure Pipelines. I noticed you had some comments in your `azure-pipelines.yml` regarding conditional steps and possibly adding a Linux flavor. I've taken the liberty of addressing those issues.

One thing I didn't completely finish: getting Linux to publish test results. The problem is that there are directories the publish task can't read already sitting in `/tmp`. I think the right solution is to use `mktemp -d` and then use that directory in the test scripts. But that felt like a pretty invasive change that you'd want to discuss before I just powered through and did it :)

Also, the contents of `azure-Linux-35.yaml` are identical to macOS right now, because I wasn't sure what needed to differ between those environments.