Description of problem:
Run etcd upgrade playbook to upgrade etcd from v3.1.9. Upgrade failed when generate etcd backup file due to an undefined variable.

TASK [etcd : Generate etcd backup] *********************************************
task path: /usr/share/ansible/openshift-ansible/roles/etcd/tasks/backup/backup.yml:64
fatal: [x.x.x.x]: FAILED! => {"failed": true, "msg": "the field 'args' has an invalid value, which appears to include a variable that is undefined. The error was: {{ 'etcdctl' if r_etcd_common_etcd_runtime == 'host' or r_etcd_common_embedded_etcd | bool else 'docker exec etcd_container etcdctl' if r_etcd_common_etcd_runtime == 'docker' else 'runc exec etcd etcdctl' }}: {{ openshift.common.etcd_runtime }}: 'openshift' is undefined\n\nThe error appears to have been in '/usr/share/ansible/openshift-ansible/roles/etcd/tasks/backup/backup.yml': line 64, 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 etcd backup\n  ^ here\n"}

Version-Release number of the following components:
openshift-ansible-3.7.26-1.git.0.f87f1af.el7.noarch

How reproducible:
always

Steps to Reproduce:
1. Rpm install ocp with external etcd(v3.1.9)
2. Upgrade etcd
# ansible-playbook -i hosts playbooks/byo/openshift-cluster/upgrades/upgrade_etcd.yml
3.

Actual results:
Upgrade etcd failed.

Expected results:
Upgrade etcd succeed.

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