[python docs] image refs broken in multiple tutorials

[aaronmarkham]

Description

Sphinx builds of the Python API docs have the following warning(s):

/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/training/normalization/index.ipynb:471: WARNING: image file not readable: tutorials/packages/gluon/training/normalization/./imgs/NCHW_IN.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/training/normalization/index.ipynb:472: WARNING: image file not readable: tutorials/packages/gluon/training/normalization/./imgs/NTC_IN.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/training/normalization/index.ipynb:471: WARNING: image file not readable: tutorials/packages/gluon/training/normalization/./imgs/NCHW_IN.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/training/normalization/index.ipynb:472: WARNING: image file not readable: tutorials/packages/gluon/training/normalization/./imgs/NTC_IN.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/training/normalization/index.ipynb:471: WARNING: image file not readable: tutorials/packages/gluon/training/normalization/./imgs/NCHW_IN.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/training/normalization/index.ipynb:472: WARNING: image file not readable: tutorials/packages/gluon/training/normalization/./imgs/NTC_IN.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/training/learning_rates/learning_rate_schedules.ipynb:173: WARNING: Duplicate substitution definition name: "png".
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/training/learning_rates/learning_rate_schedules.ipynb:201: WARNING: Duplicate substitution definition name: "png".
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/training/learning_rates/learning_rate_schedules.ipynb:242: WARNING: Duplicate substitution definition name: "png".
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/training/learning_rates/learning_rate_schedules_advanced.ipynb:241: WARNING: Duplicate substitution definition name: "png".
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/training/learning_rates/learning_rate_schedules_advanced.ipynb:300: WARNING: Duplicate substitution definition name: "png".
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/training/learning_rates/learning_rate_schedules_advanced.ipynb:364: WARNING: Duplicate substitution definition name: "png".
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/training/learning_rates/learning_rate_schedules_advanced.ipynb:424: WARNING: Duplicate substitution definition name: "png".
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/training/learning_rates/learning_rate_schedules_advanced.ipynb:487: WARNING: Duplicate substitution definition name: "png".
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/training/learning_rates/learning_rate_schedules_advanced.ipynb:513: WARNING: Duplicate substitution definition name: "png".
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/loss/loss.ipynb:465: WARNING: image file not readable: tutorials/packages/gluon/loss/triplet_loss.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/loss/loss.ipynb:466: WARNING: image file not readable: tutorials/packages/gluon/loss/ctc_loss.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/image/mnist.ipynb:425: WARNING: Duplicate substitution definition name: "png".
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/loss/custom-loss.ipynb:269: WARNING: image file not readable: tutorials/packages/gluon/loss/images/inuktitut_1.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/loss/custom-loss.ipynb:372: WARNING: image file not readable: tutorials/packages/gluon/loss/images/inuktitut_2.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/autograd/index.ipynb:176: WARNING: image file not readable: _static/autograd/autograd_gradient.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/autograd/index.ipynb:177: WARNING: image file not readable: _static/autograd/autograd_forward_backward.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/autograd/index.ipynb:436: WARNING: image file not readable: _static/autograd/autograd_control_flow.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/autograd/index.ipynb:495: WARNING: image file not readable: _static/autograd/autograd_control_flow_grad.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/blocks/activations/activations.ipynb:162: WARNING: image file not readable: tutorials/packages/gluon/blocks/activations/images/sigmoid.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/blocks/activations/activations.ipynb:189: WARNING: image file not readable: tutorials/packages/gluon/blocks/activations/images/tanh.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/blocks/activations/activations.ipynb:224: WARNING: image file not readable: tutorials/packages/gluon/blocks/activations/images/softsign.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/blocks/activations/activations.ipynb:254: WARNING: image file not readable: tutorials/packages/gluon/blocks/activations/images/relu.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/blocks/activations/activations.ipynb:288: WARNING: image file not readable: tutorials/packages/gluon/blocks/activations/images/softrelu.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/blocks/activations/activations.ipynb:313: WARNING: image file not readable: tutorials/packages/gluon/blocks/activations/images/leakyrelu.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/blocks/activations/activations.ipynb:349: WARNING: image file not readable: tutorials/packages/gluon/blocks/activations/images/prelu.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/blocks/activations/activations.ipynb:387: WARNING: image file not readable: tutorials/packages/gluon/blocks/activations/images/elu.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/blocks/activations/activations.ipynb:416: WARNING: image file not readable: tutorials/packages/gluon/blocks/activations/images/selu.png
/work/mxnet/docs/python_docs/python/build/tutorials/packages/gluon/blocks/activations/activations.ipynb:451: WARNING: image file not readable: tutorials/packages/gluon/blocks/activations/images/swish.png

How to reproduce

You can run into the problem following these steps.

1. Run a "lite" binary build.

ci/build.py --docker-registry mxnetci --platform ubuntu_cpu_lite /work/runtime_functions.sh build_ubuntu_cpu_docs

2. Run the Python API docs build:

ci/build.py --docker-registry mxnetci --platform ubuntu_cpu_python /work/runtime_functions.sh build_python_docs

[mxnet-label-bot]

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Here are my recommended label(s): Doc