Fixup manpages to reflect recent change in serno path

serno is now '/dev/disk/by-serno' rather than '/dev/serno'.

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Convert '/dev/serno' to '/dev/disk/by-serno' in a few places

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>