Support MySQL authentication switch protocol.

[twocode]

Similar issues in node: https://github.com/mysqljs/mysql/issues/1729, https://github.com/mysqljs/mysql/pull/1730

MySQL Authentication switch protocol is missed in Emysql driver, this cause unavailability for Erlang client to some mysql environment such as Azure MySQL service, which relies on this protocol feature to do authentication. It also potentially breaks future authentication enforcement of sha256_password authentication.