title: Docker wait for postgresql to be running
body: <p>I am using postgresql with django in my project. I've got them in different containers and the problem is that i need to wait for postgres before running django. At this time i am doing it with <code>sleep 5</code> in <code>command.sh</code> file for django container. I also found that netcat can do the trick but I would prefer way without additional packages. <code>curl</code> and <code>wget</code> can't do this because they do not support postgres protocol.
  Is there a way to do it?</p>