Avoid using nvidia-smi on a CPU-only Colab instance

[FlorianVal]

What does this PR do?

On a CPU-only Colab notebook, nvidia-smi is not available. Running notebook_launcher was running into an error because of that, assuming that we were using Colab with a GPU.

The fix check first if torch has detected a GPU, if so it goes on with the usual check with nvidia-smi, if there is no GPU, the code does not run nvidia-smi as it is not available.

Not sure how to add tests here as it is in a specific env, open to suggestions :)

Fixes #3871

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Who can review?

@SunMarc ?

[SunMarc]

Thanks !

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