Reset storageConfiguration at CoreFeature tearDown

The CoreFeature is not "symmetric", it calls the StorageConfiguration constructor in its start method but only the first time, thus when running a test suite (like we do in Studio with MultiStudioRunner), the second test will fail because all the properties injected in the OSGiRuntimeService by the StorageConfiguration constructor are not present anymore (because the runtime context has been properly reseted).

The solution: reset the storageConfiguration in a stop method in CoreFeature