[SSSD] [PATCH] Improve negcache with subdomains

[Jakub Hrozek]

Hi,

I noticed this bug while working on the SSH fix with
default_domain_suffix. It turns out our filter_users/filter_groups don't
work well in this scenario, which might have effect on the server load
even. Attached are patches that re-initialize negcache with filter_lists
contents after the subdomains are (re)discovered. All patches have
tests.