Harden TestLoadNoNamespaceClass

TestLoadNoNamespaceClass was also testing the ability to load the FFITarget. This isn't ideal for a system test.

This PR hardens the test so that if the library is already loaded it doesn't attempt to reload it.

It should be followed up by a cleanup PR to:

   - Add a support method to libraryServices: IsLibraryLoaded
   - Fix the libraryServices.Reset support method
Merge pull request #2493 from DynamoDS/fixFlakyFFILibraryTest

Harden TestLoadNoNamespaceClass