nss: sssd returns '/' for emtpy home directories
For empty home directory in passwd file sssd returns "/". Sssd
should respect system behaviour and return the same as nsswitch
"files" module - return empty string.
Resolves:
https://pagure.io/SSSD/sssd/issue/3901
Reviewed-by: Simo Sorce <simo@redhat.com>
Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>
(cherry picked from commit 90f32399b4100ce39cf665649fde82d215e5eb49)