ci: use runAsUser: 0 instead of privileged: true

It's the same thing for now for backwards compatibility, but privileged
has a different connotation from "running as uid 0". See for details:
coreos/coreos-ci-lib#3

.cci.jenkinsfile

@@ -1,6 +1,6 @@
 @Library('github.com/coreos/coreos-ci-lib@master') _
 
-coreos.pod([image: 'registry.fedoraproject.org/fedora:30', privileged: true, kvm: true]) {
+coreos.pod([image: 'registry.fedoraproject.org/fedora:30', runAsUser: 0, kvm: true]) {
       checkout scm
 
       stage("Build") {