Evaluate how kernel memory poisoning works for disk cache

Originally created by @intrigeri on #12398 (Redmine)

See draft test procedure on #12354 (comment 49539). Work shall be based on the wip/feature/12090-slab-poisoning branch.

Feature Branch: bugfix/12354-drop-kexec-memory-wipe

Edited May 15, 2020 by intrigeri

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