if the unionfs backend was changed to btrfs, it would fail to remove old overlayfs dirs

git-svn-id: https://svn.qindel.com/repos/main/projects/qindel/QVD/src/trunk@22173 4046b530-fbad-4e16-af16-ee11f0b55167
Fix  #1446: Create certs dir on startup

git-svn-id: https://svn.qindel.com/repos/main/projects/qindel/QVD/src/trunk@22179 4046b530-fbad-4e16-af16-ee11f0b55167