Don't use $HOST until it's set.

The new argument parsing leaves $HOST unset; this leaves $LOCKFILE and $LOGFILE incorrect, and backup.sh exits with an error:

    tee: /tank/rsync/hosts//l/backup.log: No such file or directory 
    /tank/rsync/bin/backup.sh: cannot create /tank/rsync/hosts//l/backup.log: No such file or directory