server: add a not-in policy for exclusion of all OSDs that don't have a
property. i.e. exclude all OSDs from china: custom.not.country = CHINA
documentation: add excludes option for custom policy attributes
servers: fixed security issue related to commit: be846aa07e9e

- admin password, super user or privileged user allows to setxattr on
xtreemfs.* attributes

- added auth-object to xattr call in the libxtreemfs for Java interface