rgw-admin: object stat also decodes policy

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
rgw: don't set shadow obj attr in object metadata

This is incorrect, was only right for pre-manifest objects.

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
rgw: fix get_obj() with zero sized obj

Now that even zero sized objs have manifest a
test had to be modified.

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
rgw: decouple bucket data pool from bucket index pool

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