Change credentials file to use python_app user

Avoi to use postgres user.

consumer/credentials.py

@@ -1,3 +1,3 @@
 def getCredentials():
     """ Return credentials for the database """
-    return "host=localhost dbname=logistics user=postgres password=postgres_password"
+    return "host=localhost dbname=logistics user=python_app password=blablapoivron"