Optimized shortfall analyzer, Autoscaler scale down optimizations

This (non-RC) release introduce the following:

• New optimizing shortfall analyzer for optimal scale up of instances. This can be chosen via scheduling service builder to override the default shortfall analyzer that is aggressive in scaling up more resources than needed.
• Optional callback hooks to Autoscaler now enable you to order the VMs that are idle for scaling down.
• Fix order of releasing of VM leases