Patch pytorch_mnist.py until torchvision issue gets resolved

See pytorch/vision#1938

Signed-off-by: Nicolas V Castet <nvcastet@us.ibm.com>

examples/pytorch_mnist.py

@@ -7,6 +7,13 @@
 import torch.utils.data.distributed
 import horovod.torch as hvd
 
+# Temporary patch this script until the MNIST dataset download issue get resolved
+# https://github.com/pytorch/vision/issues/1938
+import urllib.request
+opener = urllib.request.build_opener()
+opener.addheaders = [('User-agent', 'Mozilla/5.0')]
+urllib.request.install_opener(opener)
+
 # Training settings
 parser = argparse.ArgumentParser(description='PyTorch MNIST Example')
 parser.add_argument('--batch-size', type=int, default=64, metavar='N',