ISPN-4690 Upgrade to Scala 2.11.2

* Minor compilation adjutsments were required, including: switching
to new scala.concurrent classes added in 2.10, extend Serializable
trait instead of annotation, and use refactored Java conversion
methods.
* Scala XML module has been separated, so REST server needs a new
dependency, which it has also been added to Infinispan server as
a new module.
Change ReplicatedCHFactory to only replace leavers in updateMembers()

Uneven primary ownership should be dealt with in rebalance() only.
Delegate the isBalanced() check in DefaultRebalancePolicy to the CH factory

Allows waitForRehashToComplete() to work even if the CH factory allocated
less than numOwners owners to each segment.