Pin pynvml (#1027)

The latest version is causing an issue with nnabla. nnabla fixed the
issue, pinning while waiting for new version of nnabla:
sony/nnabla#892

http://b/190622765

Author: rosbo

gpu.Dockerfile

@@ -100,6 +100,8 @@ RUN pip install /tmp/tfa_gpu/tensorflow*.whl && \
 RUN pip install pycuda && \
     pip install cupy-cuda$CUDA_MAJOR_VERSION$CUDA_MINOR_VERSION && \
     pip install pynvrtc && \
+    # b/190622765 latest version is causing issue. nnabla fixed it in https://github.com/sony/nnabla/issues/892, waiting for new release before we can remove this pin.
+    pip install pynvml==8.0.4 && \
     pip install nnabla-ext-cuda$CUDA_MAJOR_VERSION$CUDA_MINOR_VERSION && \
     /tmp/clean-layer.sh