[Merge] ~lamoura/update-notifier:update-esm-handling into update-notifier:master

[Lucas Albuquerque Medeiros de Moura]

Also Brian, I have updated the `is_esm_distro` logic here. I couldn't find any gaps on it, but if you want to double check if it sound, that would be great.
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https://code.launchpad.net/~lamoura/update-notifier/+git/update-notifier/+merge/401002
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