Bug 1564365

Description of problem:

In https://docs.openshift.com/container-platform/3.9/install_config/aggregate_logging.html#aggregate-logging-ansible-variables only a selected number of variables is mentioned and documented. But when checking https://github.com/openshift/openshift-ansible/blob/23c461de43fe9c82b4ef6941216436ef9ff6c9f7/roles/openshift_logging/tasks/install_logging.yaml we can see that there are many more variables that can be used and set.

It would therefore be nice to have them all covered and documented in https://docs.openshift.com/container-platform/3.9/install_config/aggregate_logging.html#aggregate-logging-ansible-variables so that people know the default value, can easily use them and thus utilize the flexibility they are providing.

Specifically have a look at the `vars` defined/specified in https://github.com/openshift/openshift-ansible/blob/23c461de43fe9c82b4ef6941216436ef9ff6c9f7/roles/openshift_logging/tasks/install_logging.yaml#L95-L335

Version-Release number of selected component (if applicable):

 - Red Hat OpenShift Container Platform 3.9 (https://docs.openshift.com/container-platform/3.9/welcome/index.html)


How reproducible:

 - Always

Steps to Reproduce:
1. Check https://docs.openshift.com/container-platform/3.9/install_config/aggregate_logging.html#aggregate-logging-ansible-variables and look for `openshift_logging_elasticsearch_storage_type` or `openshift_logging_elasticsearch_hostmount_path`

Actual results:

No entry available. Means customer does not know it exists and can be used and customer does also not know it's default value

Expected results:

All Variables available in https://github.com/openshift/openshift-ansible/blob/23c461de43fe9c82b4ef6941216436ef9ff6c9f7/roles/openshift_logging/tasks/install_logging.yaml#L95-L335 documented with information what they do, how to use it and default value

Additional info: