mysql-test/lib/mtr_misc.pl:
  Add function 'mtr_rmtree' it will try 'rmtree' and if that fails (most likely
  due to permission problems we will fun File::find to chmod all files and dirs
  to 0777 and then delete.
mysql-test/mysql-test-run.pl:
  Use 'mtr_rmtree' in favour of 'rmtree'