Test running Tails from an external hard disk

From Cybelle’s June spreadsheet: https://lists.torproject.org/pipermail/tor-project/2018-July/001871.html

If we want people to rely more on Tails it might be useful to some people to install Tails on a hard disk instead of a USB stick, to have more storage capacity, be faster, and more reliable.

Related issues

Related to #10731
Related to #8422
Related to #6397
Blocks #16080 (closed)

Original created by @sajolida on 15742 (Redmine)

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