Fix flaky rpl.binlog_trx_meta_data test

Summary:
Fix the race between `flush logs` and `purge logs` by syncing the slave
with the master before purging.

Reviewed By: yashtc

Differential Revision: D10247529

fbshipit-source-id: e21c618

Author: abhinav04sharma

mysql-test/suite/rpl/include/binlog_trx_meta_data.inc

@@ -1,8 +1,8 @@
 # Init
 connection master;
+flush logs;
 sync_slave_with_master;
 connection master;
-flush logs;
 let $master_last_log = query_get_value("SHOW MASTER STATUS", "File", 1);
 eval purge binary logs to '$master_last_log';
 connection slave;