OpenVINO No module named 'cv2'

[byarbrough]

This is the dreaded import cv2 error.

$make infer
sudo docker exec movrasten_app python infer/classification_sample.py -m /app/models/openvino/model.xml -nt 5 -i /app/data/infer/ -d CPU
Traceback (most recent call last):
  File "infer/classification_sample.py", line 23, in <module>
    import cv2
ModuleNotFoundError: No module named 'cv2'
Makefile:66: recipe for target 'infer' failed
make: *** [infer] Error 1

I've seen it before, as have many others, but going to try and fix it permanently this time.
ab92f8d

[byarbrough]

Multiple other issues address the same thing.
experiencor/keras-yolo2#230
opencv/opencv#7045
jazzsaxmafia/video_to_sequence#3 (comment)

After running pip install opencv-python as suggested, I was presented with a new error:

$make infer
sudo docker exec movrasten_app python infer/classification_sample.py -m /app/models/openvino/model.xml -nt 5 -i /app/data/infer/ -d CPU
Traceback (most recent call last):
  File "infer/classification_sample.py", line 23, in <module>
    import cv2
  File "/usr/local/lib/python3.6/dist-packages/cv2/__init__.py", line 3, in <module>
    from .cv2 import *
ImportError: libSM.so.6: cannot open shared object file: No such file or directory
Makefile:66: recipe for target 'infer' failed
make: *** [infer] Error 1

This led me to find more related issues:
ray-project/ray#923
NVIDIA/nvidia-docker#864 (comment)

I added apt-get install -y libsm6 libxext6 libxrender-dev to Dockerfile, now the error is:

$ make infer
sudo docker exec movrasten_app python infer/classification_sample.py -m /app/models/openvino/model.xml -nt 5 -i /app/data/infer/ -d CPU
Traceback (most recent call last):
  File "infer/classification_sample.py", line 27, in <module>
    from openvino.inference_engine import IENetwork, IEPlugin
ModuleNotFoundError: No module named 'openvino'
Makefile:67: recipe for target 'infer' failed
make: *** [infer] Error 1