Implement "decode" parameter in pull()

[D3vil0p3r]

Implement decode (bool) parameter in pull(). Decode the JSON data from the server into dicts. Only applies with stream=True.

If decode is not implemented, the output will be something like:

b'{"stream":"Trying to pull docker.io/ohmyzsh/zsh:latest...\\n"}
...

By implementing decode the pull output will be:

{'stream': 'Trying to pull docker.io/ohmyzsh/zsh:latest...\n'}

It partial covers #456

[rhatdan]

@jwhonce PTAL

[D3vil0p3r]

I also integrated a test. It can be run on integration directory by executing:

pytest test_images.py::ImagesIntegrationTest::test_pull_stream_decode

@jwhonce sorry for the ping, could you please review also this PR?

Thanks

[rhatdan]

@D3vil0p3r Could you squash your commits.

[rhatdan]

/approve
LGTM
@jwhonce @umohnani8 PTAL

[openshift-ci]

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This pull-request has been approved by: D3vil0p3r, rhatdan
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[D3vil0p3r]

@D3vil0p3r Could you squash your commits.

Thank you very much. Commit squashed.