When using a "mixed instance policy"[1] instance group spot and onDemand nodes are part of the same
ASG. The ASG handles the percentage of spot vs onDemand instances. There are no annotations, EC2 tags or labels to identify which
instances are onDemand vs spot. There is a field called `InstanceLifecycle` accessible through `EC2.DescribeInstances`.
The field `InstanceLifecycle` is available only in `spot` and
`scheduled` AWS EC2 instance types.
This PR introduces a new label to be attached on AWS EC2 spot nodes.
The label is:
```
node-role.kubernetes.io/spot-worker: "true"
```
or
```
node-role.kubernetes.io/scheduled-worker: "true"
```
[^1]: https://github.com/kubernetes/kops/blob/master/docs/instance_groups.md#mixedinstancepolicy-aws-only
John Gardiner Myers
Rodrigo Menezes
Panagiotis Atmatzidis
Justin SB