rgw: cls_log_entry has id field

The id field can be used as the marker for log list / trim
operations.

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
rgw: update log APIs to use markers

a few APIs were missing markers, fixed that.

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