message: Use the convolution pass type when allocating tensors.
  Summary:
  The input and weight allocators take a pass type.  This change
  fills in the pass type for convolutions.
  Test Plan: All existing tests ok.  conv2_tr is not made worse.
  Reviewers: georgep, jakeh
diff: @@ -475,6 +475,9 @@ static StatusOr<poplar::Tensor> AddConvolutionInput(
  auto name = StrCat(debug_name, "_input");
  poplar::OptionFlags opts;
  + opts.set("pass",
  + ConvClassificationTypeToString(target, resources.annotations));
  +
  poplar::Tensor out = poplin::createInput(graph, params, name, opts,
  &resources.convolution_cache);
  return ShuffleConvolutionInputToTensorflow(target, out);
  @@ -488,6 +491,9 @@ static StatusOr<poplar::Tensor> AddConvolutionWeights(
  auto name = StrCat(debug_name, "_weights");
  poplar::OptionFlags opts;
  + opts.set("pass",
  + ConvClassificationTypeToString(target, resources.annotations));
  +
  poplar::Tensor out = poplin::createWeights(graph, params, name, opts,
  &resources.convolution_cache);
  