Description of problem:
During an upgrade of free-int cluster, received the following error:

-------------------
TASK [openshift_metrics : generate hawkular-cassandra persistent volume claims (dynamic)] ***
task path: /home/opsmedic/aos-cd/tmp/tmp.zqPTE6bwRQ/openshift-ansible_extract/roles/openshift_metrics/tasks/install_cassandra.yaml:45
fatal: [54.145.181.193]: FAILED! => {
    "failed": true, 
    "msg": "the field 'vars' has an invalid value, which appears to include a variable that is undefined. The error was: {{ openshift_hosted_metrics_storage_labels | default(null) }}: 'null' is undefined\n\nThe error appears to have been in '/home/opsmedic/aos-cd/tmp/tmp.zqPTE6bwRQ/openshift-ansible_extract/roles/openshift_metrics/tasks/install_cassandra.yaml': line 45, column 3, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n\n- name: generate hawkular-cassandra persistent volume claims (dynamic)\n  ^ here\n"
}

PLAY RECAP *********************************************************************
54.145.181.193             : ok=82   changed=17   unreachable=0    failed=1   
localhost                  : ok=10   changed=0    unreachable=0    failed=0   
-------------------

Version-Release number of selected component (if applicable):
oc v3.6.114
kubernetes v1.6.1+5115d708d7
features: Basic-Auth GSSAPI Kerberos SPNEGO

Server https://internal.api.free-int.openshift.com:443
openshift v3.6.114
kubernetes v1.6.1+5115d708d7

(upgrading from v3.6.104)


How reproducible:
Unknown

Additional info:
Full log: https://atomic-e2e-jenkins.rhev-ci-vms.eng.rdu2.redhat.com/job/aos-cd/job/cluster%252Foperation/234/console