TL;DR: If you encounter the error, "The provided host name is not valid for this server. " while trying to install Drupal 8, and you have just created a new virtual host in Apache for your site,you may have forgotten to a2ensite your new host!
For example (in Ubuntu):
sudo a2ensite examplesite.conf
Then restart Apache for your site enable to take effect:
sudo service apache2 restart