Close java driver Cluster in CQLRR.close

patch by Mariusz Kryński; reviewed by jbellis for CASSANDRA-7228

CHANGES.txt

@@ -1,4 +1,5 @@
 2.0.9
+ * (Hadoop) Close java driver Cluster in CQLRR.close (CASSANDRA-7228)
  * Fix potential SlabAllocator yield-starvation (CASSANDRA-7133)
  * Warn when 'USING TIMESTAMP' is used on a CAS BATCH (CASSANDRA-7067)
  * Starting threads in OutboundTcpConnectionPool constructor causes race conditions (CASSANDRA-7177)

src/java/org/apache/cassandra/hadoop/cql3/CqlRecordReader.java

@@ -133,6 +133,8 @@ public class CqlRecordReader extends RecordReader<Long, Row>
     {
         if (session != null)
             session.close();
+        if (cluster != null)
+            cluster.close();
     }
 
     public Long getCurrentKey()