wait-ready should give a success message to stderr

[ZZiigguurraatt]

Right now when using wait-ready, we get periodic indication that LND is NOT ready, but then when LND is actually ready, it silently exits with exit code 0.

Would like to see another log message before exiting so we don't need to do a bunch of work to create a scenario where we can capture the exit code and see if it quit in success or failure.