sss_cache: User/groups invalidation in domain cache
    
    When a group/users are invalidated from sss_cache, the group/user
    information in domain and timestamps cache are inconsistent with
    regard to dataExpireTimestamp attribute.
    
    This patch fixes the problem by explicitly invalidating the domain
    cache's entry when the timestamp cache entry is invalidated
    by sss_cache call. There is one new function:
    * sysdb_invalidate_cache_entry()
    provided for this purpose and used only in sss_cache utility.
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/3164
    
    Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>
    Reviewed-by: Fabiano Fidêncio <fidencio@redhat.com>