Fixing the error in event publishing

This is error occurrs when the event publishing cause and error, it does not print any log.

components/mobile-plugins/android-plugin/org.wso2.carbon.device.mgt.mobile.android.api/src/main/java/org/wso2/carbon/mdm/services/android/services/impl/EventReceiverServiceImpl.java

@@ -106,9 +106,12 @@ public class EventReceiverServiceImpl implements EventReceiverService {
                 message.setResponseCode("Event is published successfully.");
                 return Response.status(Response.Status.CREATED).entity(message).build();
             } else {
+                log.warn("Error occurred while trying to publish the event. This could be due to unavailability " +
+                        "of the publishing service. Please make sure that analytics server is running and accessible by " +
+                        "this server");
                 throw new UnexpectedServerErrorException(
-                        new ErrorResponse.ErrorResponseBuilder().setCode(500l).setMessage("Error occurred while " +
-                                "publishing the event.").build());
+                        new ErrorResponse.ErrorResponseBuilder().setCode(503l).setMessage("Error occurred due to " +
+                                "unavailability of the publishing service.").build());
             }
         } catch (DataPublisherConfigurationException e) {
             String msg = "Error occurred while getting the Data publisher Service instance.";