FatTreeZone: Add limiters for switches

FatTreeZone: Add limiters for switches

Users can set limiters for switches (elements whose level > 0) in Fat-Tree.

Coordinates in Fat-tree are now characterized by: <level, id>, level 0
elements are the leaves (processing nodes).

Uniform limiter behavior in routes: src, destination and middle nodes.

Changes in tests:
1) cluster-multicpu: adjust timing due to new limiters.

2) flatifier tests must be adapted for these reasons:
  - Changed callback to create limiters from XML. Radicals in XML are valid for leaves in the tree. Use internal ID instead.
  - Changed order of links in the route from get_local_route of Fat-trees.