Title: #703: nss: sssd returns '/' for emtpy home directories
I thought that fallback_homedir = "" would work but it doesn't, not even
with escaping quotes. An empty attribute is silently ignored.
About whether we care about this use-case..I don't know, currently I don't think
See the full comment at https://github.com/SSSD/sssd/pull/703#issuecomment-444114458