PXB used to determine GTID mode on slave incorrectly, and thus generated invalid xtrabackup_slave_info.
For MariaDB PXB used `gtid_slave_pos` variable, now we use `Using_Gtid` from `SHOW SLAVE STATUS`.
For MySQL PXB used `Executed_Gtid_Set` instead of correct `Auto_Position` from `SHOW SLAVE STATUS`.
PXB used to determine GTID mode on slave incorrectly, and thus generated invalid xtrabackup_ slave_info.
For MariaDB PXB used `gtid_slave_pos` variable, now we use `Using_Gtid` from `SHOW SLAVE STATUS`.
For MySQL PXB used `Executed_Gtid_Set` instead of correct `Auto_Position` from `SHOW SLAVE STATUS`.