Respect TraitFilters

Change 1
There are a variety of properties on the TestCase.  If you look at the discovery code you'll see that it uses reflection into V12 as well (in VsDiscoveryVisitor): CreateVsTestCase calls static Action<TestCase, string, string> GetAddTraitThunk().

Also note that traits get added as an array of KeyValuePairs on TestObject.Property called "TestObject.Traits" (in TraitCollection in VS):

this.testObject.SetPropertyValue<KeyValuePair<string, string>[]>(TraitCollection.TraitsProperty, keyValuePairArray);