Description of problem:
When I create the scale group with playbook: provision_install.yml, I meet this error:
'l_epoch_time' is undefined

for that, I search the source code, and get the following result:
# grep -r  l_epoch_time  
roles/openshift_aws/tasks/scale_group.yml:    launch_config_name: "{{ openshift_aws_node_group.name }}-{{ openshift_aws_ami_map[openshift_aws_node_group.group] | default(openshift_aws_ami) }}-{{ l_epoch_time }}"

and inspect git change log, find
that fact for `l_epoch_time` was removed somehow:
# git show 6d2ab4679
... ...
-# Need to set epoch time in one place to use for launch_config and scale_group
-- set_fact:
-    l_epoch_time: "{{ ansible_date_time.epoch }}"
... ...

Version-Release number of the following components:
# git describe
openshift-ansible-3.11.0-0.20.0-20-g8fa3d80

How reproducible:
100%

Steps to Reproduce:
1. ansible-playbook -i inventory.yaml -e @provisioning_vars.yaml playbooks/aws/openshift-cluster/provision_install.yml  
2.
3.

Actual results:
TASK [openshift_aws : Create the scale group] ****************************************************************************************************
Thursday 23 August 2018  02:22:51 -0400 (0:00:00.176)       0:01:07.851 *******  
fatal: [localhost]: FAILED! => {"msg": "The task includes an option with an undefined variable. The error was: 'l_epoch_time' is undefined\n\nThe error appears to have been in '/root/openshift-ansible/roles/openshift_aws/tasks/scale_group.yml': line 14, 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: Create the scale group\n  ^ here\n"}

Expected results:
Create scale group is success

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