mds: CDir::log_mark_dirty needs to flush before waiting
mds: CDir::log_mark_dirty needs to flush before waiting

We need to flush before waiting or else our completion (and mark_diryt())
will be out of order with respect to other dir updates.

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

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