Process Incomplete Jobs

- Added a new task to process incomplete jobs
- Added tests to test the new method
- Updated the check for incomplete jobs method to start the new task

This will effectively resume tasks which for some reason were interrupted
whilst they were being processed. In some cases only some of the csv
was processed, this will find the place in the csv and continue processing
from that point.

app/config.py

@@ -50,6 +50,7 @@ class QueueNames(object):
 class TaskNames(object):
     DVLA_JOBS = 'send-jobs-to-dvla'
     DVLA_NOTIFICATIONS = 'send-api-notifications-to-dvla'
+    PROCESS_INCOMPLETE_JOBS = 'process-incomplete-jobs'
 
 
 class Config(object):