Tests:
- In development VM, add a remote backup location of "tester@localhost:~/backups".
Verify the SSH host key. plinth@freedombox key is listed in
/home/tester/.ssh/authorized_keys.
- Remove the remote backup location, and delete /home/tester/.ssh/authorized_keys.
Add the same remote backup location again. plinth@freedombox key is again
listed in /home/tester/.ssh/authorized_keys.
Signed-off-by: James Valleroy <jvalleroy@mailbox.org>