MRC: added Vivaldi coordinates to OSD/replica selection policy interface,...

MRC: added Vivaldi coordinates to OSD/replica selection policy interface, added support for setting attributes for individual policies


git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@1276 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534