Misleading error on initialise

If no remote dataset is specified:

2019-12-06 08:56:29,418::zback::DEBUG: Destination is remote 2019-12-06 08:56:29,621::zback::DEBUG: stderr: cannot open 'LIDO1-SECONDARY/ghlab-data': dataset does not exist

2019-12-06 08:56:29,622::zback::WARNING: Remote command returned stderr 2019-12-06 08:56:29,622::zback::WARNING: remote command: zfs list -H -t snap -s creation -o name -r LIDO1-SECONDARY/ghlab-data

Perhaps useful to wrap this in "Don't worry its fine" or similar...