tests: switch Jekyll tests to EL8

Keep web host on a specific EL7 version to workaround a Docker bug.

Author: duck-rh

molecule/jekyll-f30/molecule.yml renamed to molecule/jekyll-el8/molecule.yml

@@ -1,20 +1,23 @@
 ---
 scenario:
-  name: jekyll-f30
+  name: jekyll-el8
+# pin centos version to workaround a bug in Docker
+#   https://github.com/docker/for-linux/issues/835
+#   https://github.com/systemd/systemd/issues/11752
 platforms:
   - name: ansible-test-builder
     # LXD
     source:
-      alias: 'fedora/30/amd64'
+      alias: 'centos/8/amd64'
     # Docker
-    image: 'fedora:30'
+    image: 'centos:8'
   # this one is always the same
   - name: ansible-test-web
     # LXD
     source:
       alias: 'centos/7/amd64'
     # Docker
-    image: 'centos:7'
+    image: 'centos:7.6.1810'
 provisioner:
   inventory:
     group_vars: