[ONOS-5729] VirtualFlowRuleStore implementation

Changes
1. VirtualStore and AbstractVirtualStore are defined
2. SimpleFlowRuleStore is added
3. FlowRuleStoreDeligate is implemented

Change-Id: Ic1f3d25f8a52d8c9bb6bc4de67abc0d642f47c9c
diff --git a/incubator/api/src/main/java/org/onosproject/incubator/net/virtual/VirtualNetworkFlowRuleStore.java b/incubator/api/src/main/java/org/onosproject/incubator/net/virtual/VirtualNetworkFlowRuleStore.java
index faca465..0567083 100644
--- a/incubator/api/src/main/java/org/onosproject/incubator/net/virtual/VirtualNetworkFlowRuleStore.java
+++ b/incubator/api/src/main/java/org/onosproject/incubator/net/virtual/VirtualNetworkFlowRuleStore.java
@@ -24,12 +24,11 @@
 import org.onosproject.net.flow.FlowRuleEvent;
 import org.onosproject.net.flow.FlowRuleStoreDelegate;
 import org.onosproject.net.flow.TableStatisticsEntry;
-import org.onosproject.store.Store;
 
 import java.util.List;
 
 public interface VirtualNetworkFlowRuleStore
-        extends Store<FlowRuleBatchEvent, FlowRuleStoreDelegate> {
+        extends VirtualStore<FlowRuleBatchEvent, FlowRuleStoreDelegate> {
     /**
      * Returns the number of flow rule in the store.
      *