When Odoo is started with a db_user using 'postgres', the process
exits with a status 1. However, this can be bypassed when the
PGUSER environment variable is used.
This commit will prevent the usage of the 'postgres' for the
environment variable too.
Also, when trying to list db's, various methods where used to find a
suitable postgres user to get this list.
In fact, as the db cursor is available, a user is already at work.
So, in order to avoid code duplication (e.g. verify user from
environment variables), this commit removes those various method
and get the db user from the cursor.
Christophe Monniez
b2a126da84