title: override config settings when using a fat jar for spark on EMR
body: <p>I'm writing a spark application, and using sbt assembly to create a fat jar, which I can send to spark-submit (through Amazon EMR).
  My application uses typesafe-config, with a <code>reference.conf</code> file inside my <code>resources</code> directory.
  My jar is on Amazon S3, and I use the command <code>aws emr add-steps..</code> to create a new spark job (which downloads the jar to the cluster and sends it to spark-submit).
  I know that in general, I can use <code>application.conf</code> to override the settings. However, since I'm using spark (and a fat jar), I need some way to deploy my override.</p>
  
  <p>What is the recommended way of overriding the application config settings when using spark?</p>