Fix pull dns image error

roles/kubernetes-apps/ansible/defaults/main.yml

@@ -14,7 +14,7 @@ kubedns_nodes_per_replica: 10
 coredns_replicas: 2
 
 # Images
-image_arch: "{{ image_arch | default('amd64') }}"
+image_arch: amd64
 kubedns_image_repo: "gcr.io/google_containers/k8s-dns-kube-dns-{{ image_arch }}"
 kubedns_image_tag: "{{ kubedns_version }}"
 dnsmasq_nanny_image_repo: "gcr.io/google_containers/k8s-dns-dnsmasq-nanny-{{ image_arch }}"