message: dnn(test): skip checks only for unstable tests
  but execute tested functions in Layer_Test_Halide/Convolution.Accuracy
diff: @@ -16,7 +16,7 @@ using namespace cv;
  using namespace cv::dnn;
  using namespace testing;
  -static void test(Mat& input, Net& net, Backend backendId, Target targetId)
  +static void test(Mat& input, Net& net, Backend backendId, Target targetId, bool skipCheck = false)
  {
  DNNTestLayer::checkBackend(backendId, targetId);
  randu(input, -1.0f, 1.0f);
  @@ -29,16 +29,19 @@ static void test(Mat& input, Net& net, Backend backendId, Target targetId)
  net.setPreferableTarget(targetId);
  Mat outputHalide = net.forward().clone();
  + if (skipCheck)
  + return;
  +
  double l1, lInf;
  DNNTestLayer::getDefaultThresholds(backendId, targetId, &l1, &lInf);
  normAssert(outputDefault, outputHalide, "", l1, lInf);
  }
  -static void test(LayerParams& params, Mat& input, Backend backendId, Target targetId)
  +static void test(LayerParams& params, Mat& input, Backend backendId, Target targetId, bool skipCheck = false)
  {
  Net net;
  net.addLayerToPrev(params.name, params.type, params);
  - test(input, net, backendId, targetId);
  + test(input, net, backendId, targetId, skipCheck);
  }
  static testing::internal::ParamGenerator<tuple<Backend, Target> > dnnBackendsAndTargetsWithHalide()
  @@ -107,10 +110,11 @@ TEST_P(Convolution, Accuracy)
  if (backendId == DNN_BACKEND_INFERENCE_ENGINE && targetId == DNN_TARGET_MYRIAD)
  throw SkipTestException("");
  + bool skipCheck = false;
  if (cvtest::skipUnstableTests && backendId == DNN_BACKEND_OPENCV &&
  (targetId == DNN_TARGET_OPENCL || targetId == DNN_TARGET_OPENCL_FP16) &&
  kernel == Size(3, 1) && stride == Size(1, 1) && pad == Size(0, 1))
  - throw SkipTestException("Skip unstable test");
  + skipCheck = true;
  int sz[] = {outChannels, inChannels / group, kernel.height, kernel.width};
  Mat weights(4, &sz[0], CV_32F);
  @@ -139,7 +143,9 @@ TEST_P(Convolution, Accuracy)
  }
  int inpSz[] = {1, inChannels, inSize.height, inSize.width};
  Mat input(4, &inpSz[0], CV_32F);
  - test(lp, input, backendId, targetId);
  + test(lp, input, backendId, targetId, skipCheck);
  + if (skipCheck)
  + throw SkipTestException("Skip checks in unstable test");
  }
  INSTANTIATE_TEST_CASE_P(Layer_Test_Halide, Convolution, Combine(
  