Fix 'timeWriting' stat for shuffle files

Due to concurrent git branches, changes from shuffle file consolidation patch
caused the shuffle write timing patch to no longer actually measure the time,
since it requires time be measured after the stream has been closed.

core/src/main/scala/org/apache/spark/scheduler/ShuffleMapTask.scala

@@ -167,6 +167,7 @@ private[spark] class ShuffleMapTask(
       var totalTime = 0L
       val compressedSizes: Array[Byte] = shuffle.writers.map { writer: BlockObjectWriter =>
         writer.commit()
+        writer.close()
         val size = writer.fileSegment().length
         totalBytes += size
         totalTime += writer.timeWriting()
@@ -184,14 +185,16 @@ private[spark] class ShuffleMapTask(
     } catch { case e: Exception =>
       // If there is an exception from running the task, revert the partial writes
       // and throw the exception upstream to Spark.
-      if (shuffle != null) {
-        shuffle.writers.foreach(_.revertPartialWrites())
+      if (shuffle != null && shuffle.writers != null) {
+        for (writer <- shuffle.writers) {
+          writer.revertPartialWrites()
+          writer.close()
+        }
       }
       throw e
     } finally {
       // Release the writers back to the shuffle block manager.
       if (shuffle != null && shuffle.writers != null) {
-        shuffle.writers.foreach(_.close())
         shuffle.releaseWriters(success)
       }
       // Execute the callbacks on task completion.