When executing a Query_log_event that is a COMMIT query,
gtid_slave_pos is updated before other replication status
variables, so when an MTR test syncs a replica with
primaries via GTID, there is a slight window where accessing
status variables, e.g. via SHOW ALL SLAVES STATUS, results
in "stale" values because gtid_slave_pos has been updated
before the *_last_event_time fields have been updated.

This patch only fixes the test by switching from using
GTIDs to using binlog file coordinates when synchronizing
replicas with their primaries.