Copying working Keras benchmarks to dnn_benchmarks subdirectory

hpvm/test/dnn_benchmarks/keras/Benchmark.py

hpvm/test/dnn_benchmarks/keras/Config.py

hpvm/test/dnn_benchmarks/keras/alexnet.py

hpvm/test/dnn_benchmarks/keras/alexnet2.py

hpvm/test/dnn_benchmarks/keras/alexnet_imagenet.py

hpvm/test/dnn_benchmarks/keras/lenet.py

hpvm/test/dnn_benchmarks/keras/mobilenet_cifar10.py

hpvm/test/dnn_benchmarks/keras/resnet18_cifar10.py

hpvm/test/dnn_benchmarks/keras/resnet50_imagenet.py

hpvm/test/dnn_benchmarks/keras/vgg16_cifar10.py

hpvm/test/dnn_benchmarks/keras/vgg16_cifar100.py

hpvm/test/dnn_benchmarks/keras/vgg16_imagenet.py