cls_log: adjust listing api

Listing api now also gets end time and a marker.

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
rgw: track object versions between reads and writes

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
rgw: log user operations

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
rgw: new RGWRados::list_entries interface to cls_log_list

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
rgw: metadata accessor to RGWRados::time_log_list

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

Conflicts:

	src/rgw/rgw_metadata.cc
rgw: show metadata log through radosgw-admin

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