make callbacks declare needing whitelisting

this will allow for custom or v1 callbacks locally loaded to automatically be triggered as they were in 1.x

lib/ansible/plugins/callback/context_demo.py

@@ -28,7 +28,8 @@ class CallbackModule(CallbackBase):
     """
     CALLBACK_VERSION = 2.0
     CALLBACK_TYPE = 'aggregate'
-    CALLBACK_TYPE = 'context_demo'
+    CALLBACK_NAME = 'context_demo'
+    CALLBACK_NEEDS_WHITELIST = True
 
     def v2_on_any(self, *args, **kwargs):
         i = 0