[Merge] ~enr0n/ubuntu-release-upgrader:lp.1960255 into ubuntu-release-upgrader:ubuntu/main

[Brian Murray]

Review: Needs Fixing

Sorry I didn't mention this early but I think we should use the i386 messaging as a template here. The important parts being:

1) using logging.error so if we look at /var/log/dist-upgrade/main.log there will be a breadcrumb as to why the upgrade quit.
2) changing the summary message to match
3) Providing information about how much longer the release the user is running will receive updates
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https://code.launchpad.net/~enr0n/ubuntu-release-upgrader/+git/ubuntu-release-upgrader/+merge/415933
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