title: spark.sql.shuffle.partitions in spark-2.0.3 doesn't take effect
body: <p>I intend to execute a SQL based on Hive-On-Spark and the settings are as follows:</p>
  
  <pre><code>select a,b,sum(c) from tbl_a group by a,b
  </code></pre>
  
  <blockquote>
    <p>set hive.execution.engine=spark;
    set spark.sql.shuffle.partitions=1201;</p>
  </blockquote>
  
  <p>Then after the application is launched, I could only see 82 tasks running parallelized from Spark yarn webpage, which is not as expected. I've tested another more complicated SQL (with GROUP BY CUBE, nested SQL query in it) and it only yield 17 tasks at stage-2 which will cause heavy full-gc. Any idea why <code>spark.sql.shuffle.partitions</code> doesn't take any effect? Thanks!</p>