When the proxy passes the container-update headers to the object server
now include the db_state, which it already had in hand. This will be
written to async_pending and allow the object-updater to know more about
a container rather then just relying on container_path attribute.
This patch also cleans up the PUT, POST and DELETE _get_update_target
paths refactoring the call into _backend_requests, only used by these
methods, so it only happens once.
Change-Id: Ie665e5c656c7fb27b45ee7427fe4b07ad466e3e2