Add quantized ResNet50 to Glow's test suite

[bertmaher]

Last week @beicy mentioned that Caffe2 has recently added a quantized ResNet50 to the model zoo: https://github.com/caffe2/models/tree/master/resnet50_quantized. Once we support loading quantized models (#1727), we should add quantized resnet to our caffe2 model downloader (utils/download_caffe2_models.sh) and add it to run.sh to test it with image-classifier.

[rdzhabarov]

See here for addressing this issue.

[bertmaher]

@beicy Since you're working on loading quantized models I figured you might as well own this issue :)