[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/DefaultGrpcTelemetryConfig.java b/apps/openstacktelemetry/app/src/main/java/org/onosproject/openstacktelemetry/config/DefaultGrpcTelemetryConfig.java
index 7b0433e..6cee737 100644
--- a/apps/openstacktelemetry/app/src/main/java/org/onosproject/openstacktelemetry/config/DefaultGrpcTelemetryConfig.java
+++ b/apps/openstacktelemetry/app/src/main/java/org/onosproject/openstacktelemetry/config/DefaultGrpcTelemetryConfig.java
@@ -18,6 +18,7 @@
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Maps;
 import org.onosproject.openstacktelemetry.api.config.GrpcTelemetryConfig;
+import org.onosproject.openstacktelemetry.api.config.TelemetryConfig;
 
 import java.util.Map;
 import java.util.Objects;
@@ -96,10 +97,15 @@
         return Objects.hash(address, port, usePlaintext, maxInboundMsgSize, configMap);
     }
 
+    @Override
+    public TelemetryConfig.Builder createBuilder() {
+        return new DefaultBuilder();
+    }
+
     /**
      * Builder class of DefaultKafkaTelemetryConfig.
      */
-    public final class DefaultBuilder implements Builder {
+    public static final class DefaultBuilder implements Builder {
 
         private String address;
         private int port;