Explicitly load the VS assemblies on Dev15 to fix unit test debugging

[billti]

See issue description in the comment at #1524 (comment) .

This may not be the most elegant solution, or the right one long term, but it does work and is simple enough. If in the test executor process, then by loading the assemblies explicitly when it attempts to run tests, but before hitting any code that would cause .NET to try and locate the assemblies, they are already loaded when required.

[paulvanbrenk]

We should figure out who the owner is for the exe and ask them to update the app.config.

[paulvanbrenk]

some nitpicks about open { being on the wrong line, and use var instead of string.

Is there a specific reason we don't want to use Assembly.GetExecutingAssebmly and get the Location from that?

[billti]

Addressed feedback.