@Override
      public void onCompletion(ReadableStreamChannel result, Exception exception) {
        channelRef.set(result);
        exceptionRef.set(exception);
        latch.countDown();
      }
Sends the given {@link RestRequest} to the {@link GetPeersHandler} and waits for the response and returns it.
@param restRequest the {@link RestRequest} to send.
@param restResponseChannel the {@link RestResponseChannel} where headers will be set.
@return the response body as a {@link ReadableStreamChannel}.
@throws Exception
ambry-frontend/src/test/java/com/github/ambry/frontend/GetPeersHandlerTest.java