NSS: Add InvalidateGroupById handler
There are some situations where, from the backend, the NSS responder
will have to be notified to invalidate a group.
In order to achieve this in a clean way, let's add the
InvalidateGroupById handler and make use of it later in this very same
series.
Related:
https://pagure.io/SSSD/sssd/issue/2653
Signed-off-by: Fabiano FidĂȘncio <fidencio@redhat.com>
Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>