mysqldump.test calls my_print_defaults in a way that includes the systemwide
my.cnf, so the results will be beyond our control and depend on whatever the
user has in their my.cnf, namely the [mysqldump] section.

call my_print_defaults with --config-file rather than --defaults-extra-file
to prevent inclusion of system-wide defaults and use our config-file only.


mysql-test/t/mysqldump.test:
  call my_print_defaults with our setup only, do not include the systemwide
  my.cnf as that would make the results unpredictable.