Fix maven build

Change-Id: I7fe9ffc18ac27a47a23cb2960632b941e02d6176
diff --git a/incubator/protobuf/services/nb/pom.xml b/incubator/protobuf/services/nb/pom.xml
index 769bf0e..8adab7e 100644
--- a/incubator/protobuf/services/nb/pom.xml
+++ b/incubator/protobuf/services/nb/pom.xml
@@ -47,6 +47,13 @@
             <artifactId>onos-incubator-grpc-api</artifactId>
             <version>${project.version}</version>
         </dependency>
+        <dependency>
+            <groupId>org.onosproject</groupId>
+            <artifactId>onos-api</artifactId>
+            <version>${project.version}</version>
+            <classifier>tests</classifier>
+            <scope>test</scope>
+        </dependency>
 
     </dependencies>