[SPARK-21738] Thriftserver doesn't cancel jobs when session is closed

## What changes were proposed in this pull request?

When a session is closed the Thriftserver doesn't cancel the jobs which may still be running. This is a huge waste of resources.
This PR address the problem canceling the pending jobs when a session is closed.

## How was this patch tested?

The patch was tested manually.

Author: Marco Gaido <[email protected]>

Closes apache#18951 from mgaido91/SPARK-21738.

Author: mgaido91

sql/hive-thriftserver/src/main/scala/org/apache/spark/sql/hive/thriftserver/SparkExecuteStatementOperation.scala

@@ -71,9 +71,9 @@ private[hive] class SparkExecuteStatementOperation(
 
   def close(): Unit = {
     // RDDs will be cleaned automatically upon garbage collection.
-    sqlContext.sparkContext.clearJobGroup()
     logDebug(s"CLOSING $statementId")
     cleanup(OperationState.CLOSED)
+    sqlContext.sparkContext.clearJobGroup()
   }
 
   def addNonNullColumnValue(from: SparkRow, to: ArrayBuffer[Any], ordinal: Int) {
@@ -273,9 +273,6 @@ private[hive] class SparkExecuteStatementOperation(
 
   override def cancel(): Unit = {
     logInfo(s"Cancel '$statement' with $statementId")
-    if (statementId != null) {
-      sqlContext.sparkContext.cancelJobGroup(statementId)
-    }
     cleanup(OperationState.CANCELED)
   }
 
@@ -287,6 +284,9 @@ private[hive] class SparkExecuteStatementOperation(
         backgroundHandle.cancel(true)
       }
     }
+    if (statementId != null) {
+      sqlContext.sparkContext.cancelJobGroup(statementId)
+    }
   }
 }