Allow to specify time when creates a mapping event instance

Change-Id: Id4d9583a8d43d8a6e0913393d35a222b9688b0d2
diff --git a/apps/mappingmanagement/api/src/main/java/org/onosproject/mapping/DefaultMapping.java b/apps/mappingmanagement/api/src/main/java/org/onosproject/mapping/DefaultMapping.java
index a6836f8..42415ff 100644
--- a/apps/mappingmanagement/api/src/main/java/org/onosproject/mapping/DefaultMapping.java
+++ b/apps/mappingmanagement/api/src/main/java/org/onosproject/mapping/DefaultMapping.java
@@ -122,6 +122,18 @@
                 .toString();
     }
 
+    /**
+     * Returns a default mapping builder.
+     *
+     * @return builder
+     */
+    public static Builder builder() {
+        return new Builder();
+    }
+
+    /**
+     * Default mapping builder.
+     */
     public static final class Builder implements Mapping.Builder {
 
         private MappingId id;