[occm]: fix openstack getServerByName return error code

[tyiying]

Additional notes:

What this PR does / why we need it:
after upgraded occm version from v1.29 to v1.32, we found occm cannot delete node from k8s node list anymore after we remove the node from openstack

Which issue this PR fixes(if applicable):
fixes #2999 - we have fixed this issue in our product using nokia repo, but would like to fix it in the upstream.

Special notes for reviewers:
After delete the node from openstack, we expect occm delete the node from k8s node list. But we still see the node in the node list:
[cloud-admin@hotel-ncs03-control-01 ~]$ sudo kubectl get node
Enter login password:
NAME STATUS ROLES AGE VERSION
hotel-ncs03-control-01 Ready 44h v1.32.8
hotel-ncs03-control-02 Ready 44h v1.32.8
hotel-ncs03-control-03 Ready 44h v1.32.8
hotel-ncs03-edge-01 Ready 44h v1.32.8
hotel-ncs03-edge-02 Ready 44h v1.32.8
hotel-ncs03-storage-01 NotReady 44h v1.32.8 <= this should be gone
hotel-ncs03-storage-02 Ready 44h v1.32.8
hotel-ncs03-storage-03 Ready 44h v1.32.8
hotel-ncs03-worker-01 Ready 44h v1.32.8
hotel-ncs03-worker-02 Ready 44h v1.32.8
[cloud-admin@hotel-ncs03-control-01 ~]$

Here are the logs we see:
E0922 11:38:01.217813 1 node_lifecycle_controller.go:156] error checking if node hotel-ncs03-storage-01 exists: failed to find object

I did a code comparison between 1.29 and 1.32, I can see the return code from getInstance() function was causing the different behavior:
The return code is expected to be cloudprovider.InstanceNotFound for both ccm 1.29 and ccm 1.32
// InstanceExists indicates whether a given node exists according to the cloud provider
func (i *InstancesV2) InstanceExists(ctx context.Context, node *v1.Node) (bool, error) {
_, err := i.getInstance(ctx, node)
if err == cloudprovider.InstanceNotFound {
klog.V(6).Infof("instance not found for node: %s", node.Name)
return false, nil
}

Release note:

NONE

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• ✅ login: tyiying / name: Yi-Ying Tan (9708d19)

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