Kubernetes: Move to version 1.9.1

This PS moves the version of kubernetes used in the gates to v1.9.1

Change-Id: Ida17cb20b0a5ce11e03ccfafddb0f58fadda76f1

tools/gate/playbooks/vars.yaml

@@ -13,7 +13,7 @@
 # limitations under the License.
 
 version:
-  kubernetes: v1.9.0
+  kubernetes: v1.9.1
   helm: v2.7.2
   cni: v0.6.0
 

tools/images/kubeadm-aio/assets/opt/playbooks/vars.yaml

@@ -33,7 +33,7 @@ all:
     helm:
       tiller_image: gcr.io/kubernetes-helm/tiller:v2.7.0
     k8s:
-      kubernetesVersion: v1.8.0
+      kubernetesVersion: v1.9.1
       imageRepository: gcr.io/google_containers
       certificatesDir: /etc/kubernetes/pki
       selfHosted: false