upstream CI: change name of base image for CentOS and Fedora.

Building containers for CentOS and Fedora were failing due to image
download failure. The container build process was fixed by changing
the base images.

molecule/centos-8-build/molecule.yml

@@ -3,7 +3,7 @@ driver:
   name: docker
 platforms:
   - name: centos-8-build
-    image: centos:8
+    image: "centos:centos8"
     pre_build_image: true
     hostname: ipaserver.test.local
     dns_servers:

molecule/fedora-latest-build/molecule.yml

@@ -3,7 +3,7 @@ driver:
   name: docker
 platforms:
   - name: fedora-latest-build
-    image: fedora-latest
+    image: "fedora:latest"
     dockerfile: Dockerfile
     hostname: ipaserver.test.local
     dns_servers: