[Compute] Fix #5258: `az image copy`: Fix `expected not NoneType` error

[yanzhudd]

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Description

The logic of az image copy command is consisted by several Azure CLI commands. The az image show command is called first, and then the fields in the output will be used to call other commands later. This error mainly due to the hyperVGeneration field of az image show command output is null value and then passed to call other commands. Issue - close: #5258

Related command

az image copy

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• [ ] Have you run azdev style <YOUR_EXT> locally? (pip install azdev required)
• [ ] Have you run python scripts/ci/test_index.py -q locally?

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• [ ] My extension description/summary conforms to the Extension Summary Guidelines.

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[yonzhan]

Compute

[azclibot]

[Release] Update index.json for extension [ image-copy ] : https://dev.azure.com/azclitools/internal/_build/results?buildId=18035&view=results