IPA: Use search timeout, not enum timeout for searching overrides
    
    Related:
        https://fedorahosted.org/sssd/ticket/2866
    
    If the LDAP connection is still established when the client moves
    offline, we rely on the search timeout to find out the client is
    offline. The override search used the enum timeout defaults to 60 seconds.
    That caused too long delays in going offline.
    
    Reviewed-by: Sumit Bose <sbose@redhat.com>