devel branch FTBFS since aufs-dkms 4.14 is in sid

Originally created by @intrigeri on #15132 (Redmine)

The simplest fix is probably to upload the 4.13 aufs-dkms package to our custom APT repo until we’re ready to switch to 4.14 (#14976 (closed)).

Feature Branch: bugfix/15132-devel-ftbfs

Edited May 15, 2020 by intrigeri

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