Today even when no stores are configured we always use the PersistenceMangerImpl as a component. The interceptors that call it are never configured, however other key parts of the system such as state transfer still call into it. Currently PersistenceManagerImpl uses another thread for some operations until the new async store SPI can be introduced. By using a stub we won't have to worry about using another thread for such calls and the JVM should have less work to do in general.

Not to mention this should make the test suite run a bit better for tests that don't use a store.