Added update for shuffleWriteTime around spilled file cleanup in ExternalSorter

Author: Ilya Ganelin

core/src/main/scala/org/apache/spark/shuffle/sort/SortShuffleWriter.scala

@@ -88,7 +88,12 @@ private[spark] class SortShuffleWriter[K, V, C](
     } finally {
       // Clean up our sorter, which may have its own intermediate files
       if (sorter != null) {
+        val startTime = System.nanoTime()
         sorter.stop()
+        context.taskMetrics().shuffleWriteMetrics.getOrElse {
+          case Some(metrics : ShuffleWriteMetrics) =>
+            metrics.incShuffleWriteTime(System.nanoTime()-startTime)
+        }
         sorter = null
       }
     }