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
Yeah you aren't really throwing it away though since you are passing it as the cause by.  But to be honest it isn't any real deal either way :)