When one PG is lost in the metadata pool, it will seem as if arbitrary dirfrags
have been lost (and possibly other things, ignored for now). The
cephfs-data-scan tool does not presently try to reconstruct those missing
parents so these tests will fail.
Importantly, also test the case where multiple ancestry paths may exist due to
out-of-date backtraces on regular files.
Signed-off-by: Patrick Donnelly <pdonnell@ibm.com>