Fix: invoke the publish method only if the service is enabled

Change-Id: Ie127458d6c8c6689d81b37436d200580ef7133a7
diff --git a/apps/openstacktelemetry/app/src/main/java/org/onosproject/openstacktelemetry/impl/RestTelemetryManager.java b/apps/openstacktelemetry/app/src/main/java/org/onosproject/openstacktelemetry/impl/RestTelemetryManager.java
index 78dd101..f94748c 100644
--- a/apps/openstacktelemetry/app/src/main/java/org/onosproject/openstacktelemetry/impl/RestTelemetryManager.java
+++ b/apps/openstacktelemetry/app/src/main/java/org/onosproject/openstacktelemetry/impl/RestTelemetryManager.java
@@ -133,7 +133,7 @@
     public Response publish(String record) {
 
         if (target == null) {
-            log.warn("REST telemetry service has not been enabled!");
+            log.debug("REST telemetry service has not been enabled!");
             return null;
         }