SYSDB: Return ERR_NO_TS when there's no timestamp cache present
This change affects sysdb_search_ts_{users,groups} functions and is
mainly needed in order to avoid breaking our current tests due to the
changes planned for fixing https://pagure.io/SSSD/sssd/issue/3369.
Related:
https://pagure.io/SSSD/sssd/issue/3369
Signed-off-by: Fabiano FidĂȘncio <fidencio@redhat.com>
Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>