rgw/rados: fix list_objects_ordered() detection of "forward progress"

rgw/rados: fix list_objects_ordered() detection of "forward progress"

for multiple versions of the same object name, ListObjectVersions is
supposed to return versions "in the order that they were stored,
returning the most recently stored object first"

this sort order is preserved by the bucket index in cls_rgw, so
list_objects_ordered() should not expect the version ids to be sorted
lexicographically. replace the not-less-than comparison with equality

Signed-off-by: Casey Bodley <cbodley@redhat.com>
(cherry picked from commit 24f55b883e5009b032e1c0e91932a01d5d231945)