K8SSAND-1863 ⁃ startOneNodeRack does not handle decommissioned StatefulSets

[burmanm]

What happened?
k8ssandra/k8ssandra-operator#746 for more details

In short, the startOneNodePerRack is unable to handle situations where StatefulSet has 0 nodes, since it still tries to find one. It should detect that the rack is fine, since target node count is 0.

Without this check, it will do a nil pointer check and requeue forever.

Did you expect to see something different?

How to reproduce it (as minimally and precisely as possible):

Environment

• Cass Operator version:

  Insert image tag or Git SHA here

  * Kubernetes version information:

  kubectl version

  * Kubernetes cluster kind:

insert how you created your cluster: kops, bootkube, etc.

• Manifests:

insert manifests relevant to the issue

• Cass Operator Logs:

insert Cass Operator logs relevant to the issue here

Anything else we need to know?:

┆Issue is synchronized with this Jira Task by Unito
┆friendlyId: K8SSAND-1863
┆priority: Medium