[vgg] Update to official vgg16 model

[vgg] Update to official vgg16 model

Update the nntrainer and tensorflow to use official VGG16 model architecture
The FC layers setup is different as the cifar100 dataset has just 100 output classes
than 1000 classes of the imagenet.
Further, the number of epochs are reduced to 1.
When training, this can be increased appropriately.

**Self evaluation:**
1. Build test: [x]Passed [ ]Failed [ ]Skipped
2. Run test: [x]Passed [ ]Failed [ ]Skipped

Signed-off-by: Parichay Kapoor <pk.kapoor@samsung.com>