BUG #15275: Trigger don't take supperuser role into account to createrole

The following bug has been logged on the website:

Bug reference:      15275
Logged by:          Alexandre Marquis
Email address:      alexandre.marquis@mamot.gouv.qc.ca
PostgreSQL version: 10.0
Operating system:   Windows
Description:

I've got a trigger whose purpose is to create a postgres user every time an
employee is added to my employee table. If I use my SUPERUSER account to add
an employee it doesn't work because I've got NOCREATEROLE instead of
CREATEROLE. But according to the CREATE ROLE docs at
https://www.postgresql.org/docs/10/static/sql-createrole.html, " You must
have CREATEROLE privilege or be a database superuser to use this command."
so as a superuser this should work.

Thx for the help!