[ONOS-6324] Add getOrDefault method to ConsistentMap.

Change-Id: Ice7ad6260c6eb8076320ef469874c0c4ceeadc19
diff --git a/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/PartitionedAsyncConsistentMap.java b/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/PartitionedAsyncConsistentMap.java
index 6378024..9adcb33 100644
--- a/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/PartitionedAsyncConsistentMap.java
+++ b/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/PartitionedAsyncConsistentMap.java
@@ -94,12 +94,18 @@
                             Match.ifValue(true),
                             false);
     }
+
     @Override
     public CompletableFuture<Versioned<V>> get(K key) {
         return getMap(key).get(key);
     }
 
     @Override
+    public CompletableFuture<Versioned<V>> getOrDefault(K key, V defaultValue) {
+        return getMap(key).getOrDefault(key, defaultValue);
+    }
+
+    @Override
     public CompletableFuture<Versioned<V>> computeIf(K key,
             Predicate<? super V> condition,
             BiFunction<? super K, ? super V, ? extends V> remappingFunction) {