Investigate intermittent test hangs on AppVeyor

[daviwil]

Tests are randomly hanging on AppVeyor. This happens both for library and host tests. I still haven't uncovered the root of the issue yet but you can usually get past the issue by re-running the tests. This isn't a long-term solution so we'll have to uncover the root cause soon.

[daviwil]

Turning off parallelized test runs in xUnit seems to have improved this somewhat but random tests still hang at times. Will continue to investigate as issues come up.

[daviwil]

This seems to have improved a lot as many builds have completed with no issues. Eventually I may turn parallelism back on since some code changes I made recently could have resolved the core issue. We'll see how it goes.

[seesharper]

I had the same problem. Turning off parallel execution solved the problem. I think it might be related to a single core build agent which seems to be the default for open source projects at AppVeyor.

Might be related to this
http://help.appveyor.com/discussions/problems/3760-vs-runner-hangs-on-run-all

[daviwil]

Thanks Bernhard! Glad I'm not the only one who experienced this.

On that note, I haven't actually seen a test hang in a while after the async timeout change so I'm going to close this issue for now.