minor code cleaning
Move the symmetry breaking to the SliceScheduler.

This allow to control all the dimensions easily. Currently, no symmetry breaking when the profile change is not homogeneous.
Bug fix in PreserveChecker
Symetry breaking is disabled when the resource usage variation for a VM is not homogeneous.

Bug fix in PreserveChecker
code cleaning
Bug fix in spread that prevent co-located VMs to be spreaded.

In addition, remove debug stuff.