Since the related change [1] the auditor checks deleted objects in
case their tombstone is ready to be reclaimed. However, the auditor
mistakes an expired object for a deleted object because
DiskFileExpired is a subclass of DiskFileDeleted. This causes a
KeyError to be raised and logged because the expired object has no
tombstone info in the ondisk_info data structure.
This patch makes the auditor catch and ignore DiskFileExpired
exceptions before handling DiskFileDeleted exceptions.
[1] Related-Change: I3e99dc702d55a7424c6482969e03cb4afac854a4
Change-Id: I9872b6997d09dcfd8a868c4b91b9379407283b8e
Closes-Bug: #1638016