HDDS-653. TestMetadataStore#testIterator fails on Windows.

Contributed by Yiqun Lin.

hadoop-hdds/common/src/test/java/org/apache/hadoop/utils/TestMetadataStore.java

@@ -163,6 +163,8 @@ public class TestMetadataStore {
       GenericTestUtils.assertExceptionContains("Store has no more elements",
           ex);
     }
+    dbStore.close();
+    dbStore.destroy();
     FileUtils.deleteDirectory(dbDir);
 
   }