We no longer need writable home for SSH key generating

Fixes #597

Signed-off-by: Michal Čihař <michal@cihar.com>
Document that HOME is no longer needed

Signed-off-by: Michal Čihař <michal@cihar.com>
Remove no longer needed HOME setup from samples

Signed-off-by: Michal Čihař <michal@cihar.com>