Closing RestRepository to avoid a connection leak (#1781)

This commit closes the RestRepository that is sent to the ScrollQuery constructor to avoid leaking connections to
Elasticsearch when many fast scrolls are called in a tight loop.
Closes #1212

Author: masseyke

mr/src/main/java/org/elasticsearch/hadoop/rest/ScrollQuery.java

@@ -77,6 +77,7 @@ public void close() {
             if (StringUtils.hasText(scrollId)) {
                 repository.getRestClient().deleteScroll(scrollId);
             }
+            repository.close();
         }
     }
 

mr/src/test/java/org/elasticsearch/hadoop/rest/ScrollQueryTest.java

@@ -51,6 +51,7 @@ public void test() throws Exception {
         Assert.assertEquals("value", JsonUtils.query("field").apply(scrollQuery.next()[1]));
         Assert.assertFalse(scrollQuery.hasNext());
         scrollQuery.close();
+        Mockito.verify(repository).close();
         Stats stats = scrollQuery.stats();
         Assert.assertEquals(1, stats.docsReceived);
     }