Bug 1529070

Description of problem:
Run upgrade_control_plane playbook against rpm cluster from v3.7 to v3.8. Upgrade failed at TASK [openshift_version : set_fact] due to fact openshift_upgrade_target is not set on dedicated nodes hosts.

TASK [openshift_version : set_fact] ********************************************
task path: /usr/share/ansible/openshift-ansible/roles/openshift_version/tasks/main.yml:25
skipping: [-master-etcd-2.] => {
    "changed": false, 
    "skip_reason": "Conditional result was False", 
    "skipped": true
}
skipping: [-master-etcd-3.] => {
    "changed": false, 
    "skip_reason": "Conditional result was False", 
    "skipped": true
}
fatal: [-node-registry-router-1.]: FAILED! => {
    "failed": true, 
    "msg": "The conditional check 'openshift_release is defined' failed. The error was: error while evaluating conditional (openshift_release is defined): {{ openshift_upgrade_target }}: 'openshift_upgrade_target' is undefined\n\nThe error appears to have been in '/usr/share/ansible/openshift-ansible/roles/openshift_version/tasks/main.yml': line 25, column 3, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n# Normalize some values that we need in a certain format that might be confusing:\n- set_fact:\n  ^ here\n"
}
...

===========debug info
No dedicated nodes in hosts group of upgrade_control_plane.yml, but required in version.yml.
# vim playbooks/common/openshift-cluster/upgrades/v3_8/upgrade_control_plane.yml
- name: Configure the upgrade target for the common upgrade tasks
  hosts: oo_masters_to_config:oo_etcd_to_config:oo_lb_to_config
  tasks:
  - set_fact:
      openshift_upgrade_target: '3.8'
      openshift_upgrade_min: '3.7'

# vim playbooks/init/version.yml
- name: Set openshift_version for etcd, node, and master hosts
  hosts: oo_etcd_to_config:oo_nodes_to_config:oo_masters_to_config:!oo_first_master
  vars:
    openshift_version: "{{ hostvars[groups.oo_first_master.0].openshift_version }}"
  pre_tasks:
  - set_fact:
      openshift_pkg_version: -{{ openshift_version }}
    when: openshift_pkg_version is not defined
  - debug: msg="openshift_pkg_version set to {{ openshift_pkg_version }}"
  roles:
  - openshift_version




Version-Release number of the following components:
ansible-2.4.1.0-1.el7.noarch
openshift-ansible-3.8.22-1.git.0.b4a1220.el7.noarch

How reproducible:
always

Steps to Reproduce:
1. RPM install ocp v3.7
2. Upgrade masters
/usr/share/ansible/openshift-ansible/playbooks/byo/openshift-cluster/upgrades/v3_8/upgrade_control_plane.yml
3.

Actual results:
Upgrade failed.

Expected results:
Upgrade succeed.

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