No scale down on scaling activity

[hjacobs]

Do not scale down if..

• ..any ASG activity is still in progress
• ..the number of ready nodes is lower than the ASG's current DesiredCapacity (this means that a node is probably booting and not registered in the API server yet)

Also do not compensate cordoned nodes which are currently being terminated by ASG (important to support kube-node-drainer.service as introduced in zalando-incubator/kubernetes-on-aws#257).

[coveralls]

Coverage remained the same at 100.0% when pulling 0f48747 on no-scale-down-on-scaling-activity into 3dc6f6e on master.

[coveralls]

Coverage remained the same at 100.0% when pulling d09a2b3 on no-scale-down-on-scaling-activity into 3dc6f6e on master.

[coveralls]

Coverage remained the same at 100.0% when pulling f965680 on no-scale-down-on-scaling-activity into 3dc6f6e on master.

[coveralls]

Coverage remained the same at 100.0% when pulling f5fc782 on no-scale-down-on-scaling-activity into 3dc6f6e on master.