Documenting Terraform variable `az_list` explicitly (#5132)

* added az_list to README section

* added az_list to cluster.tfvars

contrib/terraform/openstack/README.md

@@ -224,6 +224,7 @@ For your cluster, edit `inventory/$CLUSTER/cluster.tfvars`.
 |Variable | Description |
 |---------|-------------|
 |`cluster_name` | All OpenStack resources will use the Terraform variable`cluster_name` (default`example`) in their name to make it easier to track. For example the first compute resource will be named`example-kubernetes-1`. |
+|`az_list` | List of Availability Zones available in your OpenStack cluster. |
 |`network_name` | The name to be given to the internal network that will be generated |
 |`network_dns_domain` | (Optional) The dns_domain for the internal network that will be generated |
 |`dns_nameservers`| An array of DNS name server names to be used by hosts in the internal subnet. |

contrib/terraform/openstack/sample-inventory/cluster.tfvars

 # your Kubernetes cluster name here
 cluster_name = "i-didnt-read-the-docs"
 
+# list of availability zones available in your OpenStack cluster
+#az_list = ["nova"]
+
 # SSH key to use for access to nodes
 public_key_path = "~/.ssh/id_rsa.pub"