It's hard to test rmiregistry and avoid "port in use" failure. Need to refactor RegistryImpl, to improve the testability.
To improve the testability of RMI, adds the method "launch", so in a subprocess of tests it could simulate rmiregistry by calling this method, then retrieve the information of returned RegistryImpl and pass back to tests, for example, get the exact port where rmiregistry is listening and pass it back to tests, this is useful when input port is 0.