Description of problem:
Cloned from https://jira.coreos.com/browse/MON-579
Create cluster-monitoring-config configmap to attach PVs, content see below

apiVersion: v1
data:
  config.yaml: |
    prometheusK8s:
      volumeClaimTemplate:
        spec:
          storageClassName: gp2
          resources:
            requests:
              storage: 2Gi
    alertmanagerMain:
      volumeClaimTemplate:
        spec:
          storageClassName: gp2
          resources:
            requests:
              storage: 2Gi
kind: ConfigMap
metadata:
  name: cluster-monitoring-config
  namespace: openshift-monitoring

# oc get sc
NAME            PROVISIONER             AGE
gp2 (default)   kubernetes.io/aws-ebs   144m

But cluster-monitoring-operator pod reports error, "spec.storage.volumeClaimTemplate.metadata.creationTimestamp in body must be of type string: "null"", details please see 
# oc -n openshift-monitoring logs cluster-monitoring-operator-89d8d78df-rlbpc | grep "openshift-monitoring/cluster-monitoring-config"
E0219 10:56:33.794706       1 operator.go:244] Syncing "openshift-monitoring/cluster-monitoring-config" failed
E0219 10:56:33.794731       1 operator.go:245] sync "openshift-monitoring/cluster-monitoring-config" failed: running task Updating Prometheus-k8s failed: reconciling Prometheus object failed: updating Prometheus object failed: Prometheus.monitoring.coreos.com "k8s" is invalid: []: Invalid value: map[string]interface {}{"apiVersion":"monitoring.coreos.com/v1", "metadata":map[string]interface {}{"name":"k8s", "namespace":"openshift-monitoring", "resourceVersion":"12632", "generation":1, "uid":"5c5e724b-3421-11e9-a787-0ad8c958fe58", "creationTimestamp":"2019-02-19T08:35:49Z", "labels":map[string]interface {}{"prometheus":"k8s"}}, "spec":map[string]interface {}{"serviceMonitorNamespaceSelector":map[string]interface {}{}, "serviceAccountName":"prometheus-k8s", "image":"quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:ba01869048bf44fc5e8c57f0a34369750ce27e3fb0b5eb47c78f42022640154c", "baseImage":"openshift/prometheus", "secrets":[]interface {}{"prometheus-k8s-tls", "prometheus-k8s-proxy", "prometheus-k8s-htpasswd", "kube-rbac-proxy"}, "resources":map[string]interface {}{}, "nodeSelector":map[string]interface {}{"beta.kubernetes.io/os":"linux"}, "ruleSelector":map[string]interface {}{"matchLabels":map[string]interface {}{"prometheus":"k8s", "role":"alert-rules"}}, "version":"v2.5.0", "storage":map[string]interface {}{"volumeClaimTemplate":map[string]interface {}{"spec":map[string]interface {}{"resources":map[string]interface {}{"requests":map[string]interface {}{"storage":"2Gi"}}, "storageClassName":"gp2", "dataSource":interface {}(nil)}, "status":map[string]interface {}{}, "metadata":map[string]interface {}{"creationTimestamp":interface {}(nil)}}}, "containers":[]interface {}{map[string]interface {}{"volumeMounts":[]interface {}{map[string]interface {}{"name":"secret-prometheus-k8s-tls", "mountPath":"/etc/tls/private"}, map[string]interface {}{"name":"secret-prometheus-k8s-proxy", "mountPath":"/etc/proxy/secrets"}, map[string]interface {}{"name":"secret-prometheus-k8s-htpasswd", "mountPath":"/etc/proxy/htpasswd"}}, "name":"prometheus-proxy", "image":"quay.io/openshift/origin-oauth-proxy:latest", "args":[]interface {}{"-provider=openshift", "-https-address=:9091", "-http-address=", "-email-domain=*", "-upstream=http://localhost:9090", "-htpasswd-file=/etc/proxy/htpasswd/auth", "-openshift-service-account=prometheus-k8s", "-openshift-sar={\"resource\": \"namespaces\", \"verb\": \"get\"}", "-openshift-delegate-urls={\"/\": {\"resource\": \"namespaces\", \"verb\": \"get\"}}", "-tls-cert=/etc/tls/private/tls.crt", "-tls-key=/etc/tls/private/tls.key", "-client-secret-file=/var/run/secrets/kubernetes.io/serviceaccount/token", "-cookie-secret-file=/etc/proxy/secrets/session_secret", "-openshift-ca=/etc/pki/tls/cert.pem", "-openshift-ca=/var/run/secrets/kubernetes.io/serviceaccount/ca.crt", "-skip-auth-regex=^/metrics"}, "ports":[]interface {}{map[string]interface {}{"name":"web", "containerPort":9091}}, "resources":map[string]interface {}{}}, map[string]interface {}{"resources":map[string]interface {}{}, "volumeMounts":[]interface {}{map[string]interface {}{"name":"secret-prometheus-k8s-tls", "mountPath":"/etc/tls/private"}, map[string]interface {}{"name":"secret-kube-rbac-proxy", "mountPath":"/etc/kube-rbac-proxy"}}, "name":"kube-rbac-proxy", "image":"quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:451274b24916b97e5ba2116dd0775cdb7e1de98d034ac8874b81c1a3b22cf6b1", "args":[]interface {}{"--secure-listen-address=0.0.0.0:9092", "--upstream=http://127.0.0.1:9095", "--config-file=/etc/kube-rbac-proxy/config.yaml", "--tls-cert-file=/etc/tls/private/tls.crt", "--tls-private-key-file=/etc/tls/private/tls.key", "--tls-cipher-suites=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,TLS_RSA_WITH_AES_128_CBC_SHA256,TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256,TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256", "--logtostderr=true", "--v=10"}, "ports":[]interface {}{map[string]interface {}{"name":"tenancy", "containerPort":9092}}}, map[string]interface {}{"image":"quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:8675adb4a2a367c9205e3879b986da69400b9187df7ac3f3fbf9882e6a356252", "args":[]interface {}{"--insecure-listen-address=127.0.0.1:9095", "--upstream=http://127.0.0.1:9090", "--label=namespace"}, "resources":map[string]interface {}{}, "name":"prom-label-proxy"}}, "affinity":map[string]interface {}{"podAntiAffinity":map[string]interface {}{"preferredDuringSchedulingIgnoredDuringExecution":[]interface {}{map[string]interface {}{"weight":100, "podAffinityTerm":map[string]interface {}{"labelSelector":map[string]interface {}{"matchExpressions":[]interface {}{map[string]interface {}{"values":[]interface {}{"k8s"}, "key":"prometheus", "operator":"In"}}}, "namespaces":[]interface {}{"openshift-monitoring"}, "topologyKey":"kubernetes.io/hostname"}}}}}, "securityContext":map[string]interface {}{}, "replicas":2, "listenLocal":true, "serviceMonitorSelector":map[string]interface {}{}, "retention":"15d", "alerting":map[string]interface {}{"alertmanagers":[]interface {}{map[string]interface {}{"namespace":"openshift-monitoring", "name":"alertmanager-main", "port":"web", "scheme":"https", "tlsConfig":map[string]interface {}{"caFile":"/etc/prometheus/configmaps/serving-certs-ca-bundle/service-ca.crt", "serverName":"alertmanager-main.openshift-monitoring.svc"}, "bearerTokenFile":"/var/run/secrets/kubernetes.io/serviceaccount/token"}}}, "externalUrl":"https://prometheus-k8s-openshift-monitoring.apps.qe-juzhao2.qe.devcluster.openshift.com/", "configMaps":[]interface {}{"serving-certs-ca-bundle", "csr-controller-ca-bundle"}}, "kind":"Prometheus"}: validation failure list:
spec.storage.volumeClaimTemplate.metadata.creationTimestamp in body must be of type string: "null"

Version-Release number of selected component (if applicable):
#oc get clusterversion
NAME      VERSION                             AVAILABLE   PROGRESSING   SINCE   STATUS
version   4.0.0-0.nightly-2019-02-20-194410   True        False         58m     Cluster version is 4.0.0-0.nightly-2019-02-20-194410

configmap-reloader: quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:037fa98f23ff812b6861675127d52eea43caa44bb138e7fe41c7199cb8d4d634
prometheus-config-reloader: quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:0b88f4c0bfc31f15d368619b951b9020853686ce46d36692f62ef437d83b1012
kube-state-metrics: quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:36f168dc7fc6ada9af0f2eeb88f394f2e7311340acc25f801830fe509fd93911
prometheus-node-exporter: quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:42be8e58f00a54b4f4cbf849203a139c93bebde8cc40e5be84305246be620350
prometheus-alertmanager: quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:455855037348f33f9810f7531d52e86450e5c75d9d06531d144abc5ac53c6786
kube-rbac-proxy: quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:4d229dee301eb7452227fefc2704b30cf58e7a7f85e0c66dd3798b6b64b79728
prometheus-operator: quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:50de7804ddd623f1b4e0f57157ce01102db7e68179c5744bac4e92c81714a881
cluster-monitoring-operator: quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:534a71a355e3b9c79ef5a192a200730b8641f5e266abe290b6f7c6342210d8a0
telemeter: quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:9021d3e9ce028fc72301f8e0a40c37e488db658e1500a790c794bfd38903bef1
prom-label-proxy: quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:90a29a928beffc938345760f88b6890dccdc6f1a6503f09fea7399469a6ca72a
prometheus: quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:ba51ac66b4c3a46d5445bdfa32f1f04b882498fe5405d88dc78a956742657105
k8s-prometheus-adapter: quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:ee79721af3078dfbcfaa75e9a47da1526464cf6685a7f4195ea214c840b59e9f
grafana: quay.io/openshift/origin-grafana:latest
oauth-proxy: quay.io/openshift/origin-oauth-proxy:latest

How reproducible:
Always

Steps to Reproduce:
1. See the description part
2.
3.

Actual results:
Failed to attach PVs for monitoring

Expected results:
Be able to attach PVs for monitoring

Additional info: