rgw: fix unordered bucket listing when object names are adorned

rgw: fix unordered bucket listing when object names are adorned

Namespaces, instances, and multipart metadata adorn object names and
are not used in the computation of an object's bucket index shard. The
logic for unordered bucket listing ignored these complexities, which
yielded incorrect results when dealing with such adorned object names.
Markers, for example, failed to continue an unordered bucket listing
where it left off and could sometimes cause listing loops.

The lifecycle rule dealing with multipart expiration exposed these
issues.

This commit makes unordered bucket listing handle these complexities.

Fixes: http://tracker.ceph.com/issues/38486
Signed-off-by: J. Eric Ivancich <ivancich@redhat.com>