ci: checkout repo into 'config' subdirectory

That way, the name of the directory is always 'config', which is what
the patterns in `kola-denylist.yaml` expects.

.cci.jenkinsfile

@@ -1,13 +1,18 @@
 // Documentation: https://github.com/coreos/coreos-ci/blob/master/README-upstream-ci.md
 
 cosaPod {
-    checkout scm
+    checkout([
+         $class: 'GitSCM',
+         branches: scm.branches,
+         extensions: scm.extensions + [[$class: 'RelativeTargetDirectory', relativeTargetDir: 'config']],
+         userRemoteConfigs: scm.userRemoteConfigs
+    ])
 
-    shwrap("ci/validate")
+    shwrap("cd config && ci/validate")
 
     shwrap("""
         mkdir -p /srv/fcos && cd /srv/fcos
-        cosa init ${env.WORKSPACE}
+        cosa init ${env.WORKSPACE}/config
         curl -LO https://raw.githubusercontent.com/coreos/fedora-coreos-releng-automation/master/scripts/download-overrides.py
         python3 download-overrides.py
         # prep from the latest builds so that we generate a diff on PRs that add packages