uclient: clean up mark_down of failed mds
uclient: clean up mark_down of failed mds

Set inst at the time we see it change, otherwise we may miss an mds that
replayed but failed before it fully recovered.

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