shrink-mds: fix condition on fs deletion

shrink-mds: fix condition on fs deletion

the new ceph status registered in `ceph_status` will report `fsmap.up` =
0 when it's the last mds given that it's done after we shrink the mds,
it means the condition is wrong. Also adding a condition so we don't try
to delete the fs if a standby node is going to rejoin the cluster.

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1787543
Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>