rgw: use shared_ptr instead of RefCountedObject

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
rgw: limit num of buckets in data changes log

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
rgw: changed data log renew thread

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