Fixed test failure that ended with "There is no group named 'mysqld.10' that can be used to resolve 'port' for test"

mysql-test/lib/My/ConfigFactory.pm:
  Added test name to error output
mysql-test/mysql-test-run.pl:
  Added testname as part of ConfigFactory for better error message
mysql-test/suite/rpl/t/rpl_test_framework.cnf:
  Added space after # to ensure that ConfigFactory treat comments as comments