packaging: Fixed default permissions for XtreemFS home directory /var/lib/xtreemfs.

This lead to a situation where the postinstall script did run chown -R xtreemfs on the whole directory tree.

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@3650 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534