title: Join RDD's to result in complement of intersection
body: <p>I have two RDD's:
  The first (User ID, Mov ID, Rating, Timestamp)</p>
  
  <pre><code>data_wo_header: RDD[String]
  scala&gt; data_wo_header.take(5).foreach(println)
  1,2,3.5,1112486027
  1,29,3.5,1112484676
  1,32,3.5,1112484819
  1,47,3.5,1112484727
  1,50,3.5,1112484580
  </code></pre>
  
  <p>and RDD2 (User ID, Mov ID)</p>
  
  <pre><code>data_test_wo_header: RDD[String]
  scala&gt; data_test_wo_header.take(5).foreach(println)
  1,2
  1,367
  1,1009
  1,1525
  1,1750
  </code></pre>
  
  <p>I need to join the two RDD's such that joining will remove the entries (UserID, Mov ID) common from RDD1.
  Can someone guide a scala-spark join for the two RDD's.
  Also I'll need a join where the new RDD derived from RDD1 has common items only.</p>