stable branch does not boot: aufs not available

Since Sep 25 most test suite scenarios fail on the stable branch with “aufs not available”.

Next steps: check the build log to see if aufs.ko was correctly built, try to reproduce locally.

This matters in case we have to release a 3.16.1 emergency release before 4.0.

Feature Branch: bugfix/17103-upgrade-linux+force-all-tests

Original created by @intrigeri on 17103 (Redmine)

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