code: public static List<Precedence> newPrecedence(VM vmBefore, Collection<VM> vmsAfter) {
          return newPrecedence(Collections.singleton(vmBefore), vmsAfter);
      }
docs: Instantiate discrete constraints to force a set of VMs to migrate after a single one.
  
  @param vmBefore the (single) VM to migrate before the others {@see vmsAfter}
  @param vmsAfter the VMs to migrate after the other one {@see vmBefore}
  @return the associated list of constraints