subdomains: inherit ldap_krb5_keytab
    
    If a non-default keytab is configured for the parent domain the
    subdomains will still use the default keytab because the alternative
    keytab is not inherited. As a consequence SSSD might not be able to
    connect to services in the subdomain because the default keytab is
    either not present or does not have suitable keys.
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>