In Debian official the MariaDB plugins (.so files) go to a separate
versioned directory so that upgrades and dependencies will work correctly.

This change extends this script to check the /usr/lib/*/mariadb19/..
directory in addition to what it already does. Without this change
the script fails with:

  $ mysql_install_db ...
  Cannot change ownership of the '/auth_pam_tool_dir' directory
  to the 'mysql' user. Check that you have the necessary permissions and
  try again.