Closes #6

When running psql commands to insert rows in the database, psql normally
returns an message about what it did, eg "INSERT 0 1" if it inserted a
row. This can be suppressed with -q . Several of the scripts use psql
commands to get primary keys from the database, inserting the row if
necessary. This can lead to the host id variable in the script being set
to 'INSERT 0 1 <thehostid>' which causes problems when this variable is
used in other SQL commands.

This always used to work; I suspect the thing that changed is our
upgrading to Postgres 16 on the backup servers, but I'm struggling to
see how as Postgres 13 seems to behave the same for me.

These are static files provided by our package, not config files.

We now e.g. have a cron job on cerebro-backup which calls
these scripts, where /sbin is not on the $PATH.

For cerebro-backup where we do backups by the directory rather than the
whole server. We need to have one machine being backed up
(cerebro-filestore) but a task per directory.

The new-backup-rsnapshot script understands a 'postgres' argument, but
this set up a postgres backup in an old style that we no longer use.
This change updates it to do some of the work of setting up a new style
postgres backup and tell the user what else they might need to edit to
make it go; it varies quite a lot depending on server.

Forcing arcfour causes us not to be able to back up jessie machines.