Start an enter password test.

* Ensure the onNext always calls the done callback so password incorrect can be tested.
* Update the server mock to use the new functions signIn and signUp.

@borjasalguero, @sergi - how is this looking for a set of tests for enter password? One thing I have changed is that onNext always calls the "done" callback whenever FxamServerRequest calls its onSuccess callback. This is so we can test things like "password incorrect" which are taken care of in the success handler instead of the error handler.