add close() method to close GraphDBConnection via GraphDBOperation, and update interface class's definition
diff --git a/src/main/java/net/onrc/onos/util/GraphDBOperation.java b/src/main/java/net/onrc/onos/util/GraphDBOperation.java
index 1d5ab20..e097bf9 100644
--- a/src/main/java/net/onrc/onos/util/GraphDBOperation.java
+++ b/src/main/java/net/onrc/onos/util/GraphDBOperation.java
@@ -271,4 +271,8 @@
 	public void rollback() {
 		conn.endTx(Transaction.ROLLBACK);
 	}
+
+	public void close() {
+		conn.close();
+	}
 }