kubeadm: upload the ClusterConfiguration during the upgrade

During the upgrade process, `kubeadm` will take the current
`ClusterConfiguration`, update the `KubernetesVersion` to the latest
version, and call to `UploadConfiguration`.

This change makes sure that when the mutation happens, not only the
`ClusterStatus` is mutated, but the `ClusterConfiguration` object
inside the `kubeadm-config` ConfigMap as well; it will contain the
new `KubernetesVersion`.

Author: ereslibre

cmd/kubeadm/app/phases/uploadconfig/uploadconfig.go

@@ -101,6 +101,10 @@ func UploadConfiguration(cfg *kubeadmapi.InitConfiguration, client clientset.Int
 			kubeadmconstants.ClusterStatusConfigMapKey:        string(clusterStatusYaml),
 		},
 	}, func(cm *v1.ConfigMap) error {
+		// Upgrade will call to UploadConfiguration with a modified KubernetesVersion reflecting the new
+		// Kubernetes version. In that case, the mutation path will take place.
+		cm.Data[kubeadmconstants.ClusterConfigurationConfigMapKey] = string(clusterConfigurationYaml)
+		// Mutate the ClusterStatus now
 		return mutateClusterStatus(cm, func(cs *kubeadmapi.ClusterStatus) error {
 			// Handle a nil APIEndpoints map. Should only happen if someone manually
 			// interacted with the ConfigMap.