Refactor LoadBalancingStrategy and its RoundRobinLoadBalancingStrategy implementation

Currently LoadBalancingStrategy.getHandlerIterator(..) method is tied to a List which is too restrictive giving the fact that its current usage is tied to a OrderedAwareLinkedHashSet thus requiring a conversion of Set to a List which is costly.
Further more, the algorithm in RoundRobinLoadBalancingStrategy is also not very efficient since it is based on creating a new ArrayList on each call.

Both could be greatly improved and preliminary testing shows significant performance improvement (3 times faster)