Task: Use TaskEvent messages

Task registry messages make more sense to use
for task events then standard registry entries
when applicable. Use them.

Tested:

    "Messages": [
        {
            "@odata.type": "#Message.v1_0_0.Message",
            "Message": "The task with id 0 has started.",
            "MessageArgs": [
                "0"
            ],
            "MessageId": "TaskEvent.1.0.1.TaskStarted",
            "Resolution": "None.",
            "Severity": "OK"
        }
    ],

Validator passed

Change-Id: I707492544e18def2833e8a2e2216ce803c42c775
Signed-off-by: James Feist <james.feist@linux.intel.com>
diff --git a/redfish-core/lib/update_service.hpp b/redfish-core/lib/update_service.hpp
index e9793eb..60d6673 100644
--- a/redfish-core/lib/update_service.hpp
+++ b/redfish-core/lib/update_service.hpp
@@ -151,14 +151,16 @@
                                         return task::completed;
                                     }
 
+                                    std::string index =
+                                        std::to_string(taskData->index);
+
                                     if (boost::ends_with(*state, "Invalid") ||
                                         boost::ends_with(*state, "Failed"))
                                     {
                                         taskData->state = "Exception";
                                         taskData->status = "Warning";
                                         taskData->messages.emplace_back(
-                                            messages::invalidObject(
-                                                "/redfish/v1/UpdateService/"));
+                                            messages::taskAborted(index));
                                         return task::completed;
                                     }
 
@@ -171,7 +173,7 @@
                                     if (boost::ends_with(*state, "Active"))
                                     {
                                         taskData->messages.emplace_back(
-                                            messages::success());
+                                            messages::taskCompletedOK(index));
                                         taskData->state = "Completed";
                                         return task::completed;
                                     }