Persist a random seed across boots

Originally created by @bertagaz on #11897 (Redmine)

Given I boot Tails from a USB stick
Then I want to have good entropy from a random seed, regardless of whether I have persistence enabled or not

Feature Branch: feature/11897-improve-random-seed-file, installer:segfault/feature/11897-Create-install-ramdom-seed

Edited May 15, 2020 by bertagaz

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