Upgrade Linux to 4.18

Originally created by @intrigeri on #15936 (Redmine)

linux-image-4.18.0-1-amd64 is now the default on sid so 4.17 (shipped in 3.9 and on current stable) won’t get any security upgrade anymore.

Feature Branch: feature/15936-linux-4.18-stable-bump-Debian+force-all-tests

Edited May 21, 2020 by intrigeri

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