title: Convert RDD[(String,List[String])] to Dataframe
body: <p>My <code>RDD</code> is in below format. i.e RDD[(String,List[String])] </p>
  
  <pre><code>(abc,List(a,b))
  (bcb,List(a,b))
  </code></pre>
  
  <p>I want to convert it to <code>Dataframe</code> Like below</p>
  
  <pre><code>col1 col2 col3
  abc   a    b
  bcb   a    b
  </code></pre>
  
  <p>what is the best approach do it in scala ?</p>