[Merge] ~osomon/software-properties:updates-refresh into software-properties:ubuntu/master

[Didier Roche]

Another test:
- if you disable main for the release pocket, it select "Custom" -> ack. However, if you then select another option like "All updates", nothing happens -> it’s still on Custom and sources.list isn’t fix
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https://code.launchpad.net/~osomon/software-properties/+git/software-properties/+merge/379345
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