Disabling a store doesn't stop it

When disabling a store via PersistenceManager.disableStore(...), the store is removed from the list of loaders/writers, but its stop() method is not called, so buffers may not be flushed.

AsyncCacheWriter will also leak the AsyncStoreCoordinator thread if stop() is not called, and this thread leak is visible when running ClassLoaderManagerDisablingTest.