BUG #15429: psql requires '-h localhost' to run basic commands

The following bug has been logged on the website:

Bug reference:      15429
Logged by:          Ryan Murphy
Email address:      murphy6239@gmail.com
PostgreSQL version: 10.5
Operating system:   Ubuntu 14.04.5 LTS
Description:

We've encountered an issue where psql requires "-h localhost" to run any
commands on PostgreSQL 10.5 machine.

$ psql --version
Error: Invalid data directory for cluster 10 main
$ psql -h localhost --version
psql (PostgreSQL) 10.5 (Ubuntu 10.5-1.pgdg14.04+1)

The issue is resolved by adding world-read access to postgresql.conf to
allow psql to read "data_directory", but this is something we've never had
to do with previous postgres versions.