code: function validateContainer (container) {
    if (!container) {
      return Boom.create(504, 'instance has no container');
    }
    if (container.error) {
      return Boom.create(504, 'instance container has error', container.error);
    }
    if (container.inspect.error) {
      return Boom.create(503, 'instance inspect failed (try again)', container.inspect.error);
    }
    return null;
  }
docs: validate container existence
  @param  {Object} container instance.attrs.container - instance container json
  @return {Error}  err       returns err only if container does not exist, else null