[tflite] label_image for tflite in Python

With model (mobilenet_v1_1.0_224_quant.tflite), input image
(grace_hooper.bmp), and labels file (labels.txt) in /tmp.
Run

```
bazel run --config opt //tensorflow/contrib/lite/examples/python:label_image
```

We can get results like

```
0.470588: military uniform
0.337255: Windsor tie
0.047059: bow tie
0.031373: mortarboard
0.019608: suit
```