Add distributed lock primitive

Change-Id: I60f4581d5acb5fc9b9a21d4191874bb56348af58
diff --git a/core/api/src/main/java/org/onosproject/store/service/DistributedPrimitive.java b/core/api/src/main/java/org/onosproject/store/service/DistributedPrimitive.java
index 8a440f3..620e16d 100644
--- a/core/api/src/main/java/org/onosproject/store/service/DistributedPrimitive.java
+++ b/core/api/src/main/java/org/onosproject/store/service/DistributedPrimitive.java
@@ -99,7 +99,12 @@
         /**
          * Transaction Context.
          */
-        TRANSACTION_CONTEXT
+        TRANSACTION_CONTEXT,
+
+        /**
+         * Distributed lock.
+         */
+        LOCK,
     }
 
     /**