Drupal 8 sub-sites gets error message: ”The provided host name is not valid for this server”

When I creates a sub-site (for Drupal 8) with aegir and look at the new sub-site I get the error ”The provided host name is not valid for this server”.
Example: I have a site called www.example.com and create a new sub-site www.example.com/internal. Then I see the error when I visit the URL www.example.com/internal.

This error message is coming from a feature that was added to Drupal 8 to protect against HTTP Host header attacks (https://www.drupal.org/node/1992030). The problem is that the trusted hosts thats is generated by Provision in provision_drupal_settings_8.tpl.php, when you have a sub-site, is not a valid host name.