public InstancesResult instanceCmd(Instances instances, String type, String name,
String start, String end, String colo) {
WebResource resource = service.path(instances.path).path(type).path(name);
resource = resource.queryParam("start", start);
if (end != null) {
resource = resource.queryParam("end", end);
}
resource = resource.queryParam("colo", colo);
return resource.header(REMOTE_USER, USER)
.accept(instances.mimeType)