Harden tron hub and recover better on exit.

We had a tron hub shutdown on 2023-07-26, triggered by the /data NFS mount going away. Recovery was pretty clean, but I don't think we can count on that.

• restarted the tron hub on pfs@mhs-ics, with {setup tron_tron; tron restart}
• found that all actors reconnected automatically, with {oneCmd.py hub actors}

  and some manual inspection. I am actually surprised this worked so well.

The /data NFS bounce also caused all the actors to stop writing their logs. Not sure how we would notice this in general...... That was fixed by telling all the non-hub actors to restart their logging via being reconfigured:

for a in $(oneCmd.py hub actors | sed -n '/actors=/{s/^.*,msg,//; s/,/ /g; p}'); do 
    echo "==== $a"
    oneCmd.py $a reloadConfiguration
    sleep 1
    oneCmd.py $a status
done

Will attach more tickets to this.