(SERVER-73) Log message when puppetserver is ready

Log a message when puppet-server's jetty server has finished
starting up and is ready to receive requests.
Nitpick but I would capitalize Puppet Server just because all/nearly-all of our log message start with an uppercase, and because it stands out just a little bit more (which seems worthwhile considering the point of doing this is to notify the user).

This will be great though, I still have to think for half a second as to whether the "Started ServerConnector..." is the log message that means it's ready. So :+1: :+1: !