Fix ganglia graphs

The graphs were broken after we changed the ganglia rrd storage location. This change fixes them by symlinking /var/lib/ganglia/rrds. Screenshot of graphs after the change.

![ganglia-screenshot](https://f.cloud.github.com/assets/143893/784198/5c7727c2-ea5f-11e2-8fa7-ac8611cb7a38.png)