container: add listclusters sample (#271)
container: add listclusters sample (#271)


adamyanliev/golang-samples,danicat/golang-samples,adamyanliev/golang-samples,GoogleCloudPlatform/golang-samples,GoogleCloudPlatform/golang-samples,danicat/golang-samples,GoogleCloudPlatform/golang-samples,danicat/golang-samples,adamyanliev/golang-samples,adamyanliev/golang-samples