title: get random rows from RDD
body: <p>I am trying to get back N random rows from a sparkSQL RDD, something like this:</p>
  
  <pre><code>sqlContext.sql("SELECT col FROM tablename").sample(true, .7, 98712).show()
  </code></pre>
  
  <p>The .7 and 98712 are just junk numbers I'm using to play with.</p>
  
  <p>I'm not really seeing random results and would like to know how to get some random rows back from an RDD?</p>