modify gitignore and kafka-debug Dockerfile

[tfnick]

because of kafka 0.10.1.0' s tgz download link is invalid, fix it.

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[sambott]

Thanks for the PR @tfnick .

The OS-specific files in the .gitignore aren't repository specific; could you move them to your local .gitignore on your machine?

Other than that, LGTM.

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