Added distributed transaction support through a two phase commit protocol

Change-Id: I85d64234a24823fee8b3c2ea830abbb6867dad38
diff --git a/core/api/src/main/java/org/onosproject/store/service/TransactionException.java b/core/api/src/main/java/org/onosproject/store/service/TransactionException.java
index 8261fbd..6135394 100644
--- a/core/api/src/main/java/org/onosproject/store/service/TransactionException.java
+++ b/core/api/src/main/java/org/onosproject/store/service/TransactionException.java
@@ -41,8 +41,14 @@
     }
 
     /**
-     * Transaction failure due to optimistic concurrency failure.
+     * Transaction failure due to optimistic concurrency violation.
      */
     public static class OptimisticConcurrencyFailure extends TransactionException {
     }
+
+    /**
+     * Transaction failure due to a conflicting transaction in progress.
+     */
+    public static class ConcurrentModification extends TransactionException {
+    }
 }
\ No newline at end of file