Update configuring_aws.adoc

Update the document to conform with:
kubernetes-retired/kube-aws#1025
https://github.com/kubernetes/kubernetes/blob/v1.8.3/pkg/cloudprovider/providers/aws/tags.go#L44-L51

install_config/configuring_aws.adoc

@@ -279,12 +279,14 @@ if you configured AWS provider credentials, you must also ensure that all
 hosts are labeled.
 
 To correctly identify which resources are associated with a cluster, tag
-resources with the key `kubernetes.io/cluster/<name>,Value=<clusterid>`, where:
+resources with the key `kubernetes.io/cluster/<clusterid>`, where:
 
-* `<name>` is a unique name for the cluster.
-* `<clusterid>` is a cluster identifier unique to the AWS Availability Zone.
+* `<clusterid>` is a unique name for the cluster.
 
-Tagging all relevant resources with the `kubernetes.io/cluster/<name>,Value=<clusterid>`
+Set the corresponding value to `owned` if the node belongs exclusively to the 
+cluster or to `shared` if it is a resource shared with other systems.
+
+Tagging all resources with the `kubernetes.io/cluster/<clusterid>,Value=(owned|shared)`
 tag avoids potential issues with multiple zones or multiple clusters.
 
 [NOTE]
@@ -308,11 +310,11 @@ There are four types of resources that need to be tagged:
 [[aws-tagging-an-existing-cluster]]
 === Tagging an Existing Cluster
 
-A cluster uses the value of the `kubernetes.io/cluster/<name>,Value=<clusterid>`
-tag to determine which resources belong to the AWS cluster. This means that all
-relevant resources must be labeled with the
-`kubernetes.io/cluster/<name>,Value=<clusterid>` using the same values for that
-key. These resources include:
+A cluster uses the value of the
+`kubernetes.io/cluster/<clusterid>,Value=(owned|shared)` tag to determine which
+resources belong to the AWS cluster. This means that all relevant resources must
+be labeled with the `kubernetes.io/cluster/<clusterid>,Value=(owned|shared)` 
+tag using the same values for that key. These resources include:
 
 * All hosts.
 * All relevant load balancers to be used in the AWS instances.