etc: Revised the default configuration files which are installed by the xtreemfs-server package.

- UUID entry was moved to the end of the file and should always stay there.
- DIR: babudb.sync mode was changed from FSYNC to FDATASYNC since this is sufficient for us.
- MRC, OSD: Added commented options as example if DIR replication is enabled and all DIR replicas have to be set.
- Changed local_clock_renewal from 50 to 0. See revision 3442 for more information.
- MRC: Removed unnecessary option 
'enable_local_FIFOs'.
- DIR, MRC: Added better explanation how to enable the BabuDB replication.
- DIR, OSD: Removed Vivaldi specific options since the default values are fine for daily usage. Instead, they are documented in the user guide now.

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@3463 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534