First, do yourself a favor and remove the /path/to/your/forums that you have listed in the first post.

Check global.php for pathnames that point to your old server. For example your old vB may have been installed in something like /var/www/html/, whereas your new box is /var/www/yourdomain.tld/httpdocs. (those are just example pathnames). Those failed to open stream errors are sometimes path/permission problems, but it's hard to tell from where I'm sitting.

As far as: php_network_getaddresses: getaddrinfo, this is possibly caused by differences between PHP on your old server and your new one, or improper PHP setup on your new host. Have a look here:

http://bugs.php.net/bug.php?id=11058

Again I'm not a developer but I'm a decent vB/Linux geek, so these are my best guesses so far. Someone more adept at troubleshooting obscure PHP/vB errors may come along and tell you that I'm completely wrong.