Add ipaUserAuthType and ipaUserAuthTypeClass
    
    This schema addition will be useful for future commits. It allows us to
    define permitted external authentication methods on both the user and
    global config. The implementation is generic, but the immediate usage
    is for otp support.
    
    https://fedorahosted.org/freeipa/ticket/3365
    http://freeipa.org/page/V3/OTP