Use new API to create Torus/Dragonfly/Fat-Tree clusters from XML.

Use new API to create Torus/Dragonfly/Fat-Tree clusters from XML.

Get rid of ClusterCreationArgs in Torus/Dragonfly/Fat-tree.

NOTE: Routers aren't created anymore for Torus/Dragonfly/Fat-tree zones.
- This router was lost in the middle of topology connected through empty
routes (no links)
- In the past, the sg_platf created a router automatically for these
netzones since they shared the same sg_platf_new_cluster function.
- Impact on flatfier test: cluster_torus.xml.