Make the stratuslab Pan templates more generic.

This is the result of our Stratuslab workshop in Paris.  These templates allowed to successfully deploy a Stratuslab cloud at UGent, using the Yum-based SPMA.

**TODO**:

* Replace `filecopy` uses with `metaconfig` (refs #3).
* Factor out the ganglia monitoring (refs #4).
* Use the Xen model for choosing the interfaces that will belong to the network bridge.

We'll tackle these during the summer, unless someone wants to contribute before.