cls_rgw: reorganize rgw_bucket_link_olh()

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>
cls_rgw: more cleanup

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>
cls_rgw: more cleanup

move versioned data and olh handling into class methods.

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>