Added System.Diagnostics.Process tests.

Added AssemblyInfo.cs file to Microsoft.Win32.Primitives, upped the version number to maximum. Tests dependent on this assembly and looking for any version of this assembly should be able to pick this up.
Fix dirs.proj to pick up csproj files that don't immediately exist under test directory but a level below.
Won't an unhandled exception fail the test case either way? I mean, we don't explicitly check everything we do to see if it failed or not elsewhere. I think we can remove the "catch" block entirely and keep the finally block if it's necessary for this stuff.

By the way, I'm all for putting up these tests as-is, considering they mirror or internal sources directly. We can improve them with changes like this separately.