Implementation of fault tolerance functions in all algorithms.

Implementation of fault tolerance functions in all algorithms.

- In DefaultMapping, it returns in both cases the next node in the list.

- In QM, it returns the best computing power node for the replacement,
  and a node from the cluster which has the most amount of free nodes
  for another node.

- In LSM (Edge-cuts), it returns the nearest node for the replacement,
  and a node from the cluster which has the most amount of free nodes
  for another node.

- Simple does the same thing as DefaultMapping.