mds: wait for rejoin_gather_finish to complete before finishing
mds: wait for rejoin_gather_finish to complete before finishing

To do that we add ourselves to the rejoin_ack_gather.  Otherwise
we end up in up:active before we've even finished our
parallel_fetch or finished up our caps!

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