Description of problem:

Trying to upgrade from 3.7 cluster to 3.9 cluster fails with following error

TASK [openshift_master : include_tasks] *********************************************************************************************************************$
task path: /root/openshift-ansible/roles/openshift_master/tasks/upgrade.yml:2
included: /root/openshift-ansible/roles/openshift_master/tasks/upgrade/rpm_upgrade.yml for ec2-35-161-124-109.us-west-2.compute.amazonaws.com

TASK [openshift_master : Upgrade master packages - yum] *****************************************************************************************************$
task path: /root/openshift-ansible/roles/openshift_master/tasks/upgrade/rpm_upgrade.yml:11
fatal: [ec2-35-161-124-109.us-west-2.compute.amazonaws.com]: FAILED! => {
    "msg": "Version comparison: 'openshift_release' is undefined"
}
        to retry, use: --limit @/root/openshift-ansible/playbooks/byo/openshift-cluster/upgrades/v3_9/upgrade.retry

PLAY RECAP **************************************************************************************************************************************************$
ec2-35-161-124-109.us-west-2.compute.amazonaws.com : ok=197  changed=14   unreachable=0    failed=1   
localhost                  : ok=19   changed=0    unreachable=0    failed=0   


Version-Release number of the following components:
rpm -q openshift-ansible 
openshift-ansible-3.7.28-1.git.0.12b5132.el7.noarch

rpm -q ansible
ansible-2.4.2.0-2.el7.noarch

ansible --version
ansible 2.4.2.0
  config file = /etc/ansible/ansible.cfg
  configured module search path = [u'/root/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python2.7/site-packages/ansible
  executable location = /usr/bin/ansible
  python version = 2.7.5 (default, Dec  8 2017, 16:39:59) [GCC 4.8.5 20150623 (Red Hat 4.8.5-25)]

How reproducible:
Always

Steps to Reproduce:
1. Create 3.7 cluster
2. upgrade to 3.9 with v3_9 playbook, inventory attached.

Actual results:
Please include the entire output from the last TASK line through the end of output if an error is generated

Expected results:
Playbook fails

Additional info:
Please attach logs from ansible-playbook with the -vvv flag