[20190501162412] Instance Termination Policies, Atomic Updates

This release adds support for fully atomic updates to Kubernetes backends and changes the instance termination priority to “newest first” in an attempt to preserve long-running tasks during autoscale.

  • #3227 atomic updates for k8s [@ddollar]
  • #3230 terminate newest instance during scale down to minimize effect on exi… [@ddollar]