sysdb: new attribute lastOnlineAuthWithCurrentToken
    
    Introduce new user attribute lastOnlineAuthWithCurrentToken.
    This attribute behaves similarly to lastOnlineAuth but is set to NULL
    after password is changed.
    
    This attribute is needed for use-case when cached authentication is used, to
    request online authentication after password is locally changed.
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/1807
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>