When loc_transport.auth_interactive_dumb() returns an exception (which was
happening on the CGD machines when a user did not set up sshkeys), fallback to
loc_transport.auth_password() instead.

I don't fully understand why auth_interactive_dumb() was failing on the CGD
machines, so I don't know if this is a general solution or if I got lucky that
it works on the CGD machines but future machines may reject both
auth_interactive_dumb() and auth_password()... hopefully it's the former.