test: Use Endpoint instead of EndpointSlice in 1.17

[nebril]

GKE keeps EndpointSlice controller disabled by default on 1.17 clusters.
This change causes tests to use Endpoint object instead of
EndpointSlice on 1.17 clusters.

fixes #14996

[nebril]

test-me-please

[pchaigno]

Also required for v1.9: https://datastudio.google.com/s/pp3gaU0V6DQ.

[aanm]

We have this code that performs the detection of endpoint slices being or not being enabled in the kube-apiserver.

cilium/pkg/k8s/version/version.go

Lines 178 to 205 in 0135e67

	func endpointSlicesFallbackDiscovery(client kubernetes.Interface) error {
	// Discovery of API groups requires the API services of the apiserver to be
	// healthy. Such API services can depend on the readiness of regular pods
	// which require Cilium to function correctly. By treating failure to
	// discover API groups as fatal, a critial loop can be entered in which
	// Cilium cannot start because the API groups can't be discovered.
	//
	// Here we acknowledge the lack of discovery ability as non Fatal and fall back to probing
	// the API directly.
	_, err := client.DiscoveryV1beta1().EndpointSlices("default").Get(context.TODO(), "kubernetes", metav1.GetOptions{})
	if err == nil {
	cached.mutex.Lock()
	cached.capabilities.EndpointSlice = true
	cached.mutex.Unlock()
	return nil
	}
	if errors.IsNotFound(err) {
	log.WithError(err).Info("Unable to retrieve EndpointSlices for default/kubernetes. Disabling EndpointSlices")
	// StatusNotFound is a safe error, EndpointSlices are
	// disabled and the agent can continue.
	return nil
	}
	// Unknown error, we can't derive whether to enable or disable
	// EndpointSlices and need to error out.
	return fmt.Errorf("unable to validate EndpointSlices support: %s", err)
	}

We need to understand if that is not enough.

[pchaigno]

@aanm This bug is currently breaking all GKE builds. Maybe we can merge this and track the apparent bug in the endpoint-slice detection separately?

[aanm]

Discussed offline, this is a bug in our tests as we expect the EndpointSlice to be available in 1.17 which is not the case for GKe.