If the user doesn't have a valid ssh key inform and keep doing
There are a few situation where set_up_user will raise an exception
if this exception is due to an invalid ssh key provided, we should
just inform the user about it and let them log in, otherwise, let's
raise the error, catch it later and inform the user then.
Signed-off-by: Pierre-Yves Chibon <email@example.com>