When Expirer is iterating task containers and doing listings, it's
possible one of the container nodes hosting the task container may
become overloaded (or have a really low backend ratelimit set).
Object-expirer should expect UnexpectedResponse and continue to try
and list the task objects in the next container.
And if the task container doesn't exist, expirer should not try to
delete the non-existent containers, before continue to work on
the next container.
Co-Authored-By: Alistair Coles <alistairncoles@gmail.com>
Change-Id: Id1966fa22725a02471e2d7c5a42fb243b1cfcf6a
7980b6a0d3