Merge pull request #2631 from ludovic-henry/fix-microsoftbuild

Merge pull request #2631 from ludovic-henry/fix-microsoftbuild

[Microsoft.Build] Fix Microsoft.Build.Execution.BuildManagerTest.BasicManualParallelBuilds

The previous implementation of ProcessWrapper would launch its own threads to read on the process stdout and stderr. We can more simply use OutputDataReceived and ErrorDataReceived which will do the same under the hood. We use as well the Exited event to track the end of the Process.