message: noticed that the user was not being created was I had it.
diff: -CREATE USER '${MAXSCALE_USERNAME:-maxscale}'@'%' identified by '${MAXSCALE_PASSWORD:-maxscale}';
  +CREATE USER '${MAXSCALE_USERNAME:-maxscale}'@'%';
  +UPDATE mysql.user SET PASSWORD=PASSWORD("${MAXSCALE_PASSWORD:-maxscale}") WHERE user="${MAXSCALE_USERNAME:-maxscale}";
  +
  GRANT SELECT ON mysql.user to '${MAXSCALE_USERNAME:-maxscale}'@'%';
  GRANT SELECT ON mysql.db TO '${MAXSCALE_USERNAME:-maxscale}'@'%';
  GRANT SELECT ON mysql.tables_priv TO '${MAXSCALE_USERNAME:-maxscale}'@'%';
  GRANT SHOW DATABASES ON *.* TO '${MAXSCALE_USERNAME:-maxscale}'@'%';
  GRANT REPLICATION SLAVE ON *.* to '${MAXSCALE_USERNAME:-maxscale}'@'%';
  GRANT REPLICATION CLIENT ON *.* to '${MAXSCALE_USERNAME:-maxscale}'@'%';
  +
  +flush privileges;
  