Have Swift storage delete segments when deleting dynamic large objects

This ensures that we reclaim the space, rather than simply deleting the manifest

Fixes https://jira.coreos.com/browse/QUAY-942

workers/chunkcleanupworker.py

@@ -20,6 +20,10 @@ class ChunkCleanupWorker(QueueWorker):
     storage_location = job_details['location']
     storage_path = job_details['path']
 
+    if not storage.exists([storage_location], storage_path):
+      logger.debug('Chunk already deleted')
+      return
+
     try:
       storage.remove([storage_location], storage_path)
     except IOError: