mariadb: handle error 1594

[ip1981]

Error 1594 ("Relay log read failure: Could not parse relay log event entry. The possible reasons are: the master's binary log is corrupted") can be recovered automatically:

1. Get Relay_Master_Log_File and Exec_Master_Log_Pos from mysql -e 'show slave status\G'.
2. Stop slave.
3. Change master log file and position: CHANGE MASTER TO MASTER_LOG_FILE=Relay_Master_Log_File, MASTER_LOG_POS=Exec_Master_Log_Pos;.
4. Start slave.