template: Fix link to CMS-specfic CernVM

Addresses #185
OK, good.  You can maybe mention also that their "latest" image is now older than their "RC4" image... which is not good.  If there is any "latest" at all, then it should rather be a symbolic link always pointing to the latest file available.

```
CMS-OpenData-RC4.ova	15-Sep-2014 19:38 	14M	 
CMS OpenData.ova	    14-May-2014 11:29 	14M	 
CMS OpenData Latest.ova	18-Jun-2014 19:17 	14M	 
CMS OpenData RC1.ova	10-Sep-2014 17:58 	14M	 
```