ISPN-4574 PartitionHandling: consider less than numOwners partitions

https://issues.jboss.org/browse/ISPN-4574

* Merge PartitionHandlingStrategy with RebalancePolicy -> AvailabilityStrategy
* Add a stable topology with the last topology that didn't need rebalancing
* NumOwnersNodeStopInSequenceTest - stop nodes gracefully instead of abruptly
I changed the interface in the meantime to receive a collection of CacheStatusResponses, each of which contains one current topology and one stable topology, so the mapping is now 1-to-1 :)