bots: Fix openshift image build

 - Drop kubevirt for now. It has been broken for many months now (#9479,
   #9638), and we must rebuild openshift to finally unbreak our cockpit/ws
   container (#9941). kubevirt tests continue to run on the
   openshift-prerelease image.

 - Move image to fedora-28, so that we can move cockpit/ws and
   cockpit/base to fedora-28.

 - Update workaround for openshift/origin#18715
   to install "openssl", which is not in the default install any more on
   Fedora 28.

Fixes #9479
Closes #9975

bots/images/scripts/openshift.bootstrap

@@ -1,4 +1,4 @@
 #! /bin/bash
 
 BASE=$(dirname $0)
-BOOTSTRAP_VOLUME_SIZE="20G" $BASE/virt-builder-fedora "$1" fedora-27 x86_64
+BOOTSTRAP_VOLUME_SIZE="20G" $BASE/virt-builder-fedora "$1" fedora-28 x86_64

bots/images/scripts/openshift.setup

@@ -154,6 +154,7 @@ update-ca-trust extract
 # multiple O= RDNs; if it's in the "wrong" order, create a new admin
 # certificate that swaps it around
 # See https://github.com/openshift/origin/issues/18715
+dnf install -y openssl
 if openssl x509 -in /openshift.local.config/master/admin.crt -text | grep -q 'Subject:.*system:cluster-admins.*system:masters'; then
     echo "Regenerating admin certificate to work around https://github.com/openshift/origin/issues/18715"
     pushd /openshift.local.config/master/
@@ -304,11 +305,14 @@ printf 'AuthorizedKeysCommand /usr/local/bin/authorized-kube-keys --kubeconfig=/
 # Pull down remaining images
 /var/lib/testvm/docker-images.setup
 
-# Prepare Kubevirt for later installation
-/var/lib/testvm/kubevirt.setup
+# kubevirt is currently uninstallable: https://github.com/cockpit-project/cockpit/pull/9638
+if [ -n "$PRERELEASE" ]; then
+    # Prepare Kubevirt for later installation
+    /var/lib/testvm/kubevirt.setup
 
-# use the pristine kube config; kubevirt.setup changes it
-cp /openshift.local.config/master/admin.kubeconfig /root/.kube/config
+    # use the pristine kube config; kubevirt.setup changes it
+    cp /openshift.local.config/master/admin.kubeconfig /root/.kube/config
+fi
 
 dnf install -y cockpit-system