boot.sh: Make way for non-kubeadm related metadata

Signed-off-by: Ian Campbell <ijc@docker.com>

Author: Ian Campbell

boot.sh

@@ -85,7 +85,11 @@ fi
 mkdir -p "${state}"
 touch $state/metadata.json
 if [ -n "${kubeadm_data}" ] ; then
-    echo "{ \"kubeadm\": { \"entries\": { ${kubeadm_data} } } }" > $state/metadata.json
+    metadata="${metadata:+$metadata, }\"kubeadm\": { \"entries\": { ${kubeadm_data} } }"
+fi
+if [ -n "${metadata}" ] ; then
+    metadata="{ ${metadata} }"
+    echo "${metadata}" > $state/metadata.json
 fi
 
 exec linuxkit run ${KUBE_RUN_ARGS} -networking ${KUBE_NETWORKING} -cpus ${KUBE_VCPUS} -mem ${KUBE_MEM} -state "${state}" -disk size=${KUBE_DISK} -data-file $state/metadata.json ${uefi} "${img}${suffix}"