Description of problem:
Try the new Metrics install way using Ansible, failed at step task TASK [openshift_metrics : Check that hawkular_metrics_hostname is set] *********
task path: openshift-ansible/roles/openshift_metrics/tasks/install_metrics.yaml:2

var name here is 'openshift_metrics_hawkular_hostname', in the README.md the var name is 'openshift_metrics_hostname', thus user follow doc and run ansible task fail.


Version-Release number of selected component (if applicable):
openshift v3.5.0.6+87f6173

How reproducible:
always

Steps to Reproduce:
1. prepare the inventory file

[oo_first_master]
$MASTER ansible_user=root ansible_ssh_user=root ansible_ssh_private_key_file="/home/penli/.ssh/libra.pem" openshift_public_hostname=$MASTER

[oo_first_master:vars]
deployment_type=openshift-enterprise
openshift_release=v3.5.0
openshift_metrics_install_metrics=true

openshift_metrics_hostname=hawkular-metrics.$SUBDOMAIN
openshift_metrics_project=openshift-infra

openshift_metrics_image_prefix=registry.ops.openshift.com/openshift3/
openshift_metrics_image_version=3.5.0

2. git clone https://github.com/openshift/openshift-ansible.git

3. ansible-playbook -vvv -i ~/inventory   playbooks/common/openshift-cluster/openshift_metrics.yml

4. task fail and abort.


Expected results:
install successfully.

Additional info:
Ansible execution log attached.