[SPARK-4663][sql]add finally to avoid resource leak

Author: baishuo <vc_java@hotmail.com>

Closes #3526 from baishuo/master-trycatch and squashes the following commits:

d446e14 [baishuo] correct the code style
b36bf96 [baishuo] correct the code style
ae0e447 [baishuo] add finally to avoid resource leak

sql/core/src/main/scala/org/apache/spark/sql/parquet/ParquetTableOperations.scala

@@ -302,11 +302,14 @@ case class InsertIntoParquetTable(
       val committer = format.getOutputCommitter(hadoopContext)
       committer.setupTask(hadoopContext)
       val writer = format.getRecordWriter(hadoopContext)
-      while (iter.hasNext) {
-        val row = iter.next()
-        writer.write(null, row)
+      try {
+        while (iter.hasNext) {
+          val row = iter.next()
+          writer.write(null, row)
+        }
+      } finally {
+        writer.close(hadoopContext)
       }
-      writer.close(hadoopContext)
       committer.commitTask(hadoopContext)
       1
     }