For rolling push, wait for unregister from ELB to complete.

Details:
* Add an unregistering state and wait for the instance to be removed
  from the load balancer.
* This allows for connection draining to complete before the
  instances are terminated.
During rolling push, wait for ELB health check, if configured.

Details:
* After the instance is InService, wait for the ELB health check if
  the autoscaling group is configured for ELB health check.
Remove extra space.
Merge pull request #1 from creilly12/feature/rolling-push-enhancements

Feature/rolling push enhancements