Description of problem:

Running the openshift-logging.yaml playbook against an inventory with no value for openshift_logging_es_pv_selector fails with the following error:

============

MSG:

the field 'vars' has an invalid value, which appears to include a variable that is undefined. The error was: {{ openshift_logging_es_pv_selector }}: {{ openshift_hosted_logging_storage_labels | default(null) }}: 'null' is undefined
==============


The documentation (and the functionality in previous releases) indicates the default value should be None.  See:  https://github.com/openshift/openshift-ansible/blob/master/roles/openshift_logging/README.md

Version-Release number of selected component (if applicable): 3.6.116 and openshift-ansible master HEAD dfd8232ec9284c0207edad62d8cb65adee07ccd3


How reproducible: Always


Steps to Reproduce:

1.  Create a logging inventory without openshift_logging_es_pv_selector
2.  Run the byo/openshift-cluster/openshift-logging.yaml playbook


Actual results:

Install fails with message above

Expected results:

openshift_logging_es_pv_selector has a default value of None

Additional info:

[oo_first_master:vars]
openshift_deployment_type=openshift-enterprise
openshift_release=v3.6.0

openshift_logging_install_logging=true
openshift_logging_use_ops=false
openshift_logging_master_url=https://ec2-34-209-212-239.us-west-2.compute.amazonaws.com:8443
openshift_logging_master_public_url=https://ec2-34-209-212-239.us-west-2.compute.amazonaws.com:8443
openshift_logging_kibana_hostname=kibana.example.com
openshift_logging_namespace=logging
openshift_logging_image_prefix=registry.ops.openshift.com/openshift3/
openshift_logging_image_version=v3.6.116
openshift_logging_es_pvc_dynamic=true
openshift_logging_es_pvc_size=50Gi
openshift_logging_fluentd_use_journal=true
openshift_logging_es_pv_selector=None