DiskFile already fills in the _ondisk_info attribute when it tries to open
a diskfile - even if the DiskFile's fileset is not valid or deleted.
During this process the rsync tempfiles would be discovered and logged,
but no-one would attempt to clean them up - even if they were really old.
Instead of logging and ignoring unexpected files when validate a DiskFile
fileset we'll add unexpected files to the unexpected key in the
_ondisk_info attribute.
With a little bit of re-organization in the auditor's object_audit method
to get things into a single return path we can add an unconditional check
for unexpected files and remove those that are "old enough".
Since the replicator will kill any rsync processes that are running longer
than the configured rsync_timeout we know that any rsync tempfiles older
than this can be deleted.
Split unlink_older_than in common.utils into two functions to allow an
explicit list of previously discovered paths to be passed in to avoid an
extra listdir. Since the getmtime handling already ignores OSError
there's less concern of race condition where a previous discovered
unexpected file is reaped by rsync while we're attempting to clean it up.
Update some doc on the new config option.
Closes-Bug: #1554005
Change-Id: Id67681cb77f605e3491b8afcb9c69d769e154283
1d03803a85