SPARK-1770: Revert accidental(?) fix

Looks like this change was accidentally committed here: https://github.com/apache/spark/commit/06b15baab25951d124bbe6b64906f4139e037deb
but the change does not show up in the PR itself (#704).

Other than not intending to go in with that PR, this also broke the test JavaAPISuite.repartition.

Author: Aaron Davidson <aaron@databricks.com>

Closes #716 from aarondav/shufflerand and squashes the following commits:

b1cf70b [Aaron Davidson] SPARK-1770: Revert accidental(?) fix

core/src/main/scala/org/apache/spark/rdd/RDD.scala

@@ -330,9 +330,9 @@ abstract class RDD[T: ClassTag](
     if (shuffle) {
       // include a shuffle step so that our upstream tasks are still distributed
       new CoalescedRDD(
-        new ShuffledRDD[Int, T, (Int, T)](map(x => (Utils.random.nextInt(), x)),
+        new ShuffledRDD[T, Null, (T, Null)](map(x => (x, null)),
         new HashPartitioner(numPartitions)),
-        numPartitions).values
+        numPartitions).keys
     } else {
       new CoalescedRDD(this, numPartitions)
     }