[PATCH] Add peer authentication TAP test

Hi hackers,

During the work in [1] we created a new TAP test to test the SYSTEM_USER 
behavior with peer authentication.

It turns out that there is currently no TAP test for the peer 
authentication, so we think (thanks Michael for the suggestion [2]) that 
it's better to split the work in [1] between "pure" SYSTEM_USER related 
work and the "pure" peer authentication TAP test work.

That's the reason of this new thread, please find attached a patch to 
add a new TAP test for the peer authentication.

[1]: 
https://www.postgresql.org/message-id/flat/7e692b8c-0b11-45db-1cad-3afc5b57409f%40amazon.com

[2]: https://www.postgresql.org/message-id/YwgboqQUV1%2BY/k6z%40paquier.xyz

Regards,

-- 
Bertrand Drouvot
Amazon Web Services: https://aws.amazon.com