Improve log for START SLAVE [SQL_THREAD] [UNTIL].

Hi,

when I ran START SLAVE SQL_THREAD UNTIL followed by another START SLAVE SQL_THREAD UNTIL in MariaDB 10.2.12, I get below in the error logs:

2018-01-20 20:38:45 139935682348800 [Note] Slave SQL thread stopped because it reached its UNTIL position <binlog pos>

2018-01-20 20:38:47 139935682348800 [Note] Slave SQL thread exiting, replication stopped in log '<binlog name>' at position <binlog pos>

2018-01-20 20:38:47 139934327043840 [Note] Slave SQL thread initialized, starting replication in log '<binlog name>' at position <binlog pos>, relay log '<relay log name>' position: <relay log pos

Notice that the log about "reached its UNTIL position" does not include a binlog filename, it would be useful to add this.

Also, notice that the log about "Slave SQL thread exiting" does not include a relay log filename and position (contrarily to the line about Slave SQL thread initialized), it would be useful to add this.

Many thanks,

JFG