MariaDB auth protocol differs from MySQL

MySQL has silently changed its server implementation of the authentication protocol in https://github.com/mysql/mysql-server/commit/2a8ce5e5c606. New protocol is a subset of the old one, some packets that were valid before are no longer valid.

They did not change libmysqlclient, so MySQL client can talk to MariaDB just fine.

But at least some third party clients implement new, stricter, protocol. For compatibility with these clients we'll MariaDB server to follow MySQL change.