Add persistence option to ECMap

Work towards ONOS-1337

Change-Id: I24e6a42e2f8856b363e79786829c51344797b81b
diff --git a/core/api/src/main/java/org/onosproject/store/service/EventuallyConsistentMapBuilder.java b/core/api/src/main/java/org/onosproject/store/service/EventuallyConsistentMapBuilder.java
index 779c329..75ac27d 100644
--- a/core/api/src/main/java/org/onosproject/store/service/EventuallyConsistentMapBuilder.java
+++ b/core/api/src/main/java/org/onosproject/store/service/EventuallyConsistentMapBuilder.java
@@ -166,6 +166,16 @@
     public EventuallyConsistentMapBuilder<K, V> withFasterConvergence();
 
     /**
+     * Configure the map to persist data to disk.
+     * <p>
+     * The default behavior is no persistence
+     * </p>
+     *
+     * @return this EventuallyConsistentMapBuilder
+     */
+    public EventuallyConsistentMapBuilder<K, V> withPersistence();
+
+    /**
      * Builds an eventually consistent map based on the configuration options
      * supplied to this builder.
      *