Refactor code

- Created TaskNames for DVLA_FILES rather than have DVLA_FILES in QueueNames
- Removed PROCESS_FTP from all_queues() as this was causing problems in picking up letter job tasks
- Created test to ensure that we don't arbitrarily add queue names to all_queues

app/config.py

@@ -30,7 +30,6 @@ class QueueNames(object):
     RETRY = 'retry-tasks'
     NOTIFY = 'notify-internal-tasks'
     PROCESS_FTP = 'process-ftp-tasks'
-    DVLA_FILES = 'send-files-to-dvla'
 
     @staticmethod
     def all_queues():
@@ -48,6 +47,10 @@ class QueueNames(object):
         ]
 
 
+class TaskNames(object):
+    DVLA_FILES = 'send-files-to-dvla'
+
+
 class Config(object):
     # URL of admin app
     ADMIN_BASE_URL = os.environ['ADMIN_BASE_URL']