[ONOS-7683] Add unit tests for a set of telemetry config classes

Change-Id: I73ad36e02044371a2fb87540e28ef2257a6dba92
diff --git a/apps/openstacktelemetry/app/src/main/java/org/onosproject/openstacktelemetry/config/DefaultRestTelemetryConfig.java b/apps/openstacktelemetry/app/src/main/java/org/onosproject/openstacktelemetry/config/DefaultRestTelemetryConfig.java
index b11b14e..29e9a2a 100644
--- a/apps/openstacktelemetry/app/src/main/java/org/onosproject/openstacktelemetry/config/DefaultRestTelemetryConfig.java
+++ b/apps/openstacktelemetry/app/src/main/java/org/onosproject/openstacktelemetry/config/DefaultRestTelemetryConfig.java
@@ -18,6 +18,7 @@
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Maps;
 import org.onosproject.openstacktelemetry.api.config.RestTelemetryConfig;
+import org.onosproject.openstacktelemetry.api.config.TelemetryConfig;
 
 import java.util.Map;
 import java.util.Objects;
@@ -114,10 +115,15 @@
                 responseMediaType, configMap);
     }
 
+    @Override
+    public TelemetryConfig.Builder createBuilder() {
+        return new DefaultBuilder();
+    }
+
     /**
      * Builder class of DefaultRestTelemetryConfig.
      */
-    public final class DefaultBuilder implements Builder {
+    public static final class DefaultBuilder implements Builder {
 
         private String address;
         private int port;