mon: remove rank from failed when taking over for failed node
mon: remove rank from failed when taking over for failed node

Leaving it there leaves a broken MDSMap, and prevents rejoin because
MDSMap::is_rejoining() is always false.

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

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