Escape output of pg_amcheck test

Escape output of pg_amcheck test

The pg_amcheck test reports a skip message if the layout of the index
does not match expectations.  That message includes the bytes that
were expected and the ones that were found.  But the found ones are
arbitrary bytes, which can have funny effects on the terminal when
they are printed.  To avoid that, escape non-word characters before
printing.

Reviewed-by: Aleksander Alekseev <aleksander@timescale.com>
Discussion: https://www.postgresql.org/message-id/flat/3f96f079-64e5-468a-8a19-cb481f0d31e5%40eisentraut.org