Add a unit test setting file to mitigate minutes long mstest initial loa...

Like we discussed, let us introduce a new setting file with much less deployment items (particularly excluding the "..\Package\Debug"). This will save 30 seconds to minutes of the initial VS test engine loading time. A very favorable relief when you just run/debug a unit test.
Of course, for scenario test, you might still need to switch to other heavyweight setting file, but if you just do code and testing, the slim version should be good enough