Code review comment for lp:~longbow/percona-xtrabackup/fix_691090

The problem with the tests is that if innobackupex fails for whatever reasons with permissions on $mysql_datadir modified, that directory cannot be removed, because the current user has no write access. So it stays there forever.

What's worse is that a Jenkins run for this MP has already poisoned slaves. There are failures like this: http://jenkins.percona.com/view/Percona%20Xtrabackup/job/percona-xtrabackup-param/80/BUILD_TYPE=release,Host=el6-64,xtrabackuptarget=xtradb55/testReport/junit/%28root%29/t_xb_perm_stream/sh/. And there are phantom xb_perm_* test failures even when the branch being tests does not have those tests!