layers: Add default layer error message config

Allows layers to output error messages even if no vk_layer_settings.txt
config file is present. Sets defaults to LOG_MSG, error, stdout.
A layer settings file will override any default values. If no settings
file is present and an app creates a debug callback, the default
callbacks will be removed and unregistered.

Change-Id: I49f37189665816df58c258b9e9629f2bf76751c8
diff --git a/layers/threading.cpp b/layers/threading.cpp
index f5d37eb..c69a8b6 100644
--- a/layers/threading.cpp
+++ b/layers/threading.cpp
@@ -285,7 +285,7 @@
     VkResult result =
         my_data->instance_dispatch_table->CreateDebugReportCallbackEXT(instance, pCreateInfo, pAllocator, pMsgCallback);
     if (VK_SUCCESS == result) {
-        result = layer_create_msg_callback(my_data->report_data, pCreateInfo, pAllocator, pMsgCallback);
+        result = layer_create_msg_callback(my_data->report_data, false, pCreateInfo, pAllocator, pMsgCallback);
     }
     finishReadObject(my_data, instance);
     return result;