Update OpenStack doc for external cloud provider (#6252)

Now the in-tree cloud provider is deprecated and it is recommended to
the external cloud provider for OpenStack instead.
The doc described how to upgrade from the in-tree cloud provider, but
it is better to describe how to deploy the external cloud provider from
scratch instead for current situation.
This updates the OpenStack doc for this usecase.

docs/openstack.md

@@ -1,7 +1,10 @@
 OpenStack
-===============
+=========
 
-To deploy kubespray on [OpenStack](https://www.openstack.org/) uncomment the `cloud_provider` option in `group_vars/all.yml` and set it to `'openstack'`.
+The in-tree cloud provider
+--------------------------
+
+To deploy Kubespray on [OpenStack](https://www.openstack.org/) uncomment the `cloud_provider` option in `group_vars/all/all.yml` and set it to `openstack`.
 
 After that make sure to source in your OpenStack credentials like you would do when using `nova-client` or `neutron-client` by using `source path/to/your/openstack-rc` or `. path/to/your/openstack-rc`.
 
@@ -51,7 +54,7 @@ Given the port ids on the left, you can set the two `allowed-address`(es) in Ope
   openstack port set e5ae2045-a1e1-4e99-9aac-4353889449a7 --allowed-address ip-address=10.233.0.0/18 --allowed-address ip-address=10.233.64.0/18
   ```
 
-If all the VMs in the tenant correspond to kubespray deployment, you can "sweep run" above with:
+If all the VMs in the tenant correspond to Kubespray deployment, you can "sweep run" above with:
 
   ```bash
   openstack port list --device-owner=compute:nova -c ID -f value | xargs -tI@ openstack port set @ --allowed-address ip-address=10.233.0.0/18 --allowed-address ip-address=10.233.64.0/18
@@ -59,21 +62,21 @@ If all the VMs in the tenant correspond to kubespray deployment, you can "sweep
 
 Now you can finally run the playbook.
 
-Upgrade from the in-tree to the external cloud provider
----------------
+The external cloud provider
+---------------------------
 
-The in-tree cloud provider is deprecated and will be removed in a future version of Kubernetes. The target release for removing all remaining in-tree cloud providers is set to 1.21
+The in-tree cloud provider is deprecated and will be removed in a future version of Kubernetes. The target release for removing all remaining in-tree cloud providers is set to 1.21.
 
 The new cloud provider is configured to have Octavia by default in Kubespray.
 
-- Change cloud provider from `cloud_provider: openstack` to the new external Cloud provider:
+- Enable the new external cloud provider in `group_vars/all/all.yml`:
 
   ```yaml
   cloud_provider: external
   external_cloud_provider: openstack
   ```
 
-- Enable Cinder CSI:
+- Enable Cinder CSI in `group_vars/all/openstack.yml`:
 
   ```yaml
   cinder_csi_enabled: true
@@ -105,6 +108,5 @@ The new cloud provider is configured to have Octavia by default in Kubespray.
   - ""
   ```
 
-- Run the `upgrade-cluster.yml` playbook
-- Run the cleanup playbook located under extra_playbooks `extra_playbooks/migrate_openstack_provider.yml` (this will clean up all resources used by the old cloud provider)
-- You can remove the feature gates for Volume migration. If you want to enable the possibility to expand CSI volumes you could leave the `ExpandCSIVolumes=true` feature gate
+- Run `source path/to/your/openstack-rc` to read your OpenStack credentials like `OS_AUTH_URL`, `OS_USERNAME`, `OS_PASSWORD`, etc. Those variables are used for accessing OpenStack from the external cloud provider.
+- Run the `cluster.yml` playbook