Drop the need for dedicated temporary storage space for IUKs on rsync.lizard

Originally created by @intrigeri on #17412 (Redmine)

That’s the second step of sysadmin#17385 (comment 3031), i.e. make it so temporary data is stored directly in /srv during the release process.

One idea could be to:

give every RM permission to SSH into rsync.lizard as the rsync_tails user, and point $HOME for this user somewhere under /srv
adjust the release process so that all SSH operations done on rsync.lizard are done as the rsync_tails user
drop the /home LV and migrate the corresponding data back to /

Edited May 15, 2020 by intrigeri

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