kubernetes: disable for architectures other than x86-64

Those images are hardcoded to use amd64 binaries.

Partially-Implements: blueprint multiarch-and-arm64-containers

Depends-On: I71ddb7ef57c64d2505cac96724b1ab6772a57d6a

Change-Id: I477b62e32a940cb93c3747f593504d861ac137bc

docker/kube/kube-base/Dockerfile.j2

@@ -3,6 +3,13 @@ MAINTAINER {{ maintainer }}
 
 ENV KUBERNETES_VERSION=v1.5.4
 
+{% if base_arch != 'x86_64' %}
+
+RUN echo 'Kubernetes images not yet available for {{ base_arch }}' \
+    && /bin/false
+
+{% endif %}
+
 ENV KUBERNETES_DOWNLOAD_ROOT=https://storage.googleapis.com/kubernetes-release/release/${KUBERNETES_VERSION}/bin/linux/amd64
 
 {% block kube_base_header %}{% endblock %}