Adds a retry mechanism when deleting containers

Bulk middleware now has a mechanism to retry a delete when the
HTTP response code is 409. This happens when the container still
has objects. It can be useful in a bulk delete where you delete
all the objects in a container and then try to delete the container.
It is very likely that at the end it will fail because the replica
objects have not been deleted by the time the middleware got a
successful response.

Change-Id: I1614fcb5cc511be26a9dda90753dd08ec9546a3c
Closes-Bug: #1253478
Merge "Adds a retry mechanism when deleting containers"