force Vagrant to use the "new" API URL

It seems Vagrant has introduced a new API and their proprietary client
does use that by default now, so they turned off the old one (or the
redirect, I really have no idea what was there last week).

Just setting the new URL (which I found out by using `vagrant --debug`)
as the server URL works for now, so let's do that, and at least unblock
nightlies.

roles/forklift/tasks/up.yml

@@ -29,6 +29,8 @@
       command: "vagrant up --no-parallel {{ forklift_boxes.keys()|join(' ') }}"
       args:
         chdir: "{{ forklift_directory }}"
+      environment:
+        VAGRANT_SERVER_URL: https://vagrantcloud.com/api/v2/vagrant
   always:
     - name: Remove lock file
       ansible.builtin.file:

vagrant/boxes.d/00-centos.yaml

@@ -1,4 +1,14 @@
 boxes:
+  centos8-stream:
+    box_name: 'centos/stream8'
+    disk_size: 40
+    libvirt: https://cloud.centos.org/centos/8-stream/x86_64/images/CentOS-Stream-Vagrant-8-latest.x86_64.vagrant-libvirt.box
+    virtualbox: https://cloud.centos.org/centos/8-stream/x86_64/images/CentOS-Stream-Vagrant-8-latest.x86_64.vagrant-virtualbox.box
+    pty: true
+    scenarios:
+      - foreman
+      - katello
+
   centos9-stream:
     box_name: 'centos/stream9'
     disk_size: 40