Here's what I did to get this working:

Edited postgresql.conf to listen on IP
Edited pg_hba.conf to allow connections from fsat IP (for specific user and db)
firewall-cmd --permanent --add-port=5432/tcp
firewall-cmd --add-port=5432/tcp

Ok so I did fork the role on :
https://github.com/gluster/gluster.org_ansible_configuration/commit/1178caf3c2ae0ee16720cb5a76651251e6ef5ab1


and opened https://gitlab.com/osas/ansible-role-postgresql/issues/3

and pushed 

https://github.com/gluster/gluster.org_ansible_configuration/commit/e20453343929fad1e47788dfaf65e12e88b270f1

I would recommend to chime on the upstream bug so we can have a idea on how we consume the role (as I would like something that allow to not repeat ourself too much)

I didn't yet open the firewall however. I would prefer to open it just for fstat.

This works now.