Convert two more 'sh' highlight styles to 'shell-example'

This is straightforward; only one shell example remained, but as we
process the man pages via pandoc and not sphinx, it's not actually
used, we leave it as such for now.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Helga Velroyen <helgav@google.com>