rgw: list_objects() sets namespace appropriately

rgw: list_objects() sets namespace appropriately

list_objects() now uses parse_raw_oid(), so that it can set the correct
namespace. It only affects users of the function that want to get all
objects in bucket, regardless to the namespace associated with it. This
makes it so that the orphan code actually works now with namespaced
objects, and with special named objects (namely, start with underscore).

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>
(cherry picked from commit 20bd490bebf9be3553d4e25322c9544b0b090086)