Getting Master Current Binlog and Binlog Position in Replication Backup
Surprise, you can get the Master's binlog file/position from the dump !!! Use --dump-slave.

MySQL 5.6 Documentation says :


  This option is similar to --master-data except that it is used to dump a replication slave server to produce a dump file that can be used to set up another server as a slave that has the same master as the dumped server. It causes the dump output to include a CHANGE MASTER TO statement that indicates the binary log coordinates (file name and position) of the dumped slave's master. These are the master server coordinates from which the slave should start replicating.


Just get the CHANGE MASTER TO command from Lines 23-25 of the dump as always.