message: remove other templating for maxscale password.
diff: CREATE USER 'maxscale'@'%';
  UPDATE mysql.user SET PASSWORD=PASSWORD("maxscale") WHERE user="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}'@'%';
  +GRANT SELECT ON mysql.user to 'maxscale'@'%';
  +GRANT SELECT ON mysql.db TO 'maxscale'@'%';
  +GRANT SELECT ON mysql.tables_priv TO 'maxscale'@'%';
  +GRANT SHOW DATABASES ON *.* TO 'maxscale'@'%';
  +GRANT REPLICATION SLAVE ON *.* to 'maxscale'@'%';
  +GRANT REPLICATION CLIENT ON *.* to 'maxscale'@'%';
  flush privileges;
  