os/kstore: we have flush_txns is to make sure read after write for the same object...

os/kstore: we have flush_txns is to make sure read after write for the same object. That's the reason why we add _txc_finalize(osr,txc) after we add the
transaction. However, since we did not call STATE_FINISHING at all, The _txf_finish will never be called and flush_txns of object will never be removed.
It will make the read on the same object hanging there forever. We will combine KV_DONE and STATE_FINISHING.

Signed-off-by: James Liu <james.liu@ssi.samsung.com>