osd: move ObjectState side effects out of do_osd_ops

osd: move ObjectState side effects out of do_osd_ops

We want to be able to handle a failure mid-way through an OSDOp
transaction and bail out with no side effects.  This patch

 * puts an ObjectState new_obs in the OoContext that modifications go in
 * only applies if it the transaction is a success
 * only does make_writeable (at the end!) if the transaction is a success

There are still side effects with the watch/notify stuff, though.

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