osd: simplify stat
osd: simplify stat

We don't actually need to stat the object (again) since we have the size
(and mtime) in the object_info_t.  Keep the existing stat in there, tho,
and assert the answer matches for the time being, since I saw behavior
that suggested they were out of sync.  See #933.

Signed-off-by: Sage Weil <6dd34506bbd5e58221bbb3e4732d97c91f02277b@newdream.net>

ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph