rgw: let newer RGWs work with older OSDs re: cls-side filtering

rgw: let newer RGWs work with older OSDs re: cls-side filtering

Previous commits moved bucket list filtering when a delimiter was
specified to the osd/cls layer. However, since rgw's are often
upgraded before osd's are, until we reach verison ceph version 16, an
rgw cannot assume that the osd/cls did the filtering. This is
addressed in the following ways....

First rgw_cls_list_ret now indicates whether filtering was done on the
osd/cls side.

And second, the old filtering code in the rgw is maintained in
RGWRados::Bucket::List::list_objects_ordered, so it can still be
triggered when all osd's are not doing the filtering.

Once we reach ceph version 16, and there is no chance that the rgw is
working with a osd running "young" version 14 code, we can remove the
backward compatibility code in
RGWRados::Bucket::List::list_objects_ordered.

Signed-off-by: J. Eric Ivancich <ivancich@redhat.com>