Description of problem:
When scaling up etcd cluster, the playbook failed as below:
PLAY [Verify Requirements] **************************************************************************************************************************************************

TASK [Gathering Facts] ******************************************************************************************************************************************************
ok: [ec2-54-237-213-42.compute-1.amazonaws.com]

TASK [Run variable sanity checks] *******************************************************************************************************************************************
An exception occurred during task execution. To see the full traceback, use -vvv. The error was: TypeError: 'NoneType' object has no attribute '__getitem__'
fatal: [ec2-54-237-213-42.compute-1.amazonaws.com]: FAILED! => {"msg": "Unexpected failure during module execution.", "stdout": ""}



Version-Release number of the following components:
openshift-ansible-3.9.0-0.41.0.git.0.8290c01.el7.noarch
ansible-2.4.2.0-2.el7.noarch

How reproducible:
100%

Steps to Reproduce:
1.Setup an ocp-3.9 with one single etcd host. Add two new hosts to [new_etcd] group in ansible inventory file, run etcd scale-up playbook
ansible-playbook -i host /usr/share/ansible/openshift-ansible/playbooks/openshift-etcd/scaleup.yml -v


Actual results:


Expected results:

Additional info:
Ansible inventory file and detailed playbook log could be found in attachment