osd/,rados/: modify TIER_FLUSH to implicitly make an object a manifest object

osd/,rados/: modify TIER_FLUSH to implicitly make an object a manifest object

Existing object-dedup command always creates temporary object and
perform set-chunk to make the input object manifest---this is because
current tier-flush, which is called by object-dedup, works only if
the target object is manifest, otherwise it just return 0.

So, object-dedup may not work if the target is already manifest.
Moreover, it causes unnecessary overhead if the target object is not manifest.

To solve these, this commit makes existing tier-flush to
change object's state to manifest implicitly.

With this change, the only required operation when calling object-dedup
is a tier-flush and object-dedup can work with the manifest object.

Signed-off-by: Myoungwon Oh <myoungwon.oh@samsung.com>