Only consider Ready and Schedulable worker nodes in auto-node selection

[dansimone]

When no explicit oci-availability-domains is specified, the current code loops through all available worker nodes, and picks an AD that has an associated worker node. A further improvement to this logic would be to only consider nodes that are Ready and Schedulable - reducing the chances of choosing an AD whose nodes are all having issues.

[prydie]

See https://github.com/kubernetes/kubernetes/blob/0f9dfca8e76790362fe775c8eedef04f349aed7e/test/e2e/framework/util.go#L2603 for an implementation example.