Skip .DS_Store files in check_mode_recursive

Hi,

I am repeatedly encountering an annoying failing test during 'make check-world'
execution on the macOS platform: pg_resetwal with the result:

Failed test 'check PGDATA permissions'

It happens because a filesystem object .DS_Store exists in the directory.
AFAIK, MacOS manages it on its own. Given that I almost never touch this module,
it seems the OS handles it automatically.

A quick dive into the mailing list history shows that this problem has been
discovered [1] and partly fixed [2] before.

It looks like this approach might be extended to TAP tests too. In the
attachment, see the sketch of the code and a minor test to prove that it works.

[1] pg_basebackup: errors on macOS on directories with ".DS_Store" files
https://www.postgresql.org/message-id/flat/E258CE50-AB0E-455D-8AAD-BB4FE8F882FB%40gmail.com
[2] Commit d3fdfdcd1c7 'Skip .DS_Store files in server side utils'

--
regards, Andrei Lepikhov,
pgEdge