master_port after a "change master" will be set to the compiled in default value
i.e not always the same as what the master report as it's port number. 


mysql-test/mysql-test-run.pl:
  Read the master-port value from the mysqld. Used for replacing the 
  default compiled in port number in for example rpl000015
mysql-test/r/rpl000015.result:
  Update result file
mysql-test/t/rpl000015.test:
  When changing master without specifying master port, the port for master will
  be set to the compiled in default. Replace with that value