def end_async_span(kvs = {}, span)
      span.set_tags(kvs) unless kvs.empty?
      span.close
    end
def end_async_span(kvs = {}, span)
      span.set_tags(kvs) unless kvs.empty?
      span.close
    end
End an asynchronous span

 @param name [Symbol] the name of the span
 @param kvs [Hash] list of key values to be reported in the span
 @param span [Span] the span of this Async op (previously returned
   from `log_async_entry`)