message: Seed dropout with random numbers
  Test Plan: Tests pass
  Reviewers: #tensorflow, jakeh
diff: @@ -90,6 +90,12 @@ class DropoutOp : public PoplibsOpDef {
  global_seed_tensor = graph.addVariable(poplar::INT, {2});
  poputil::mapTensorLinearly(graph, global_seed_tensor);
  + // Make sure the random seed has a random number to make each operation
  + // less deterministic.
  + int random_seed[] = {std::rand(), std::rand()};
  + graph.setInitialValue(global_seed_tensor,
  + poplar::ArrayRef<int>(random_seed, 2));
  +
  // Create the literal value to add onto the seed each iteration.
  int32_t increment_literal[] = {1, 0};
  poplar::Tensor increment_tensor =
  