Correct the OpenStack plugin example config (#40766)

The current example configuration is not
quite right, so this patch implements a
fix which corrects it

The 'inventory_hostname' argument is removed
as it's the same value as the default.

(cherry picked from commit 12218f33a5)

lib/ansible/plugins/inventory/openstack.py

@@ -94,11 +94,9 @@ DOCUMENTATION = '''
 EXAMPLES = '''
 # file must be named openstack.yaml or openstack.yml
 # Make the plugin behave like the default behavior of the old script
-simple_config_file:
-    plugin: openstack
-    inventory_hostname: 'name'
-    expand_hostvars: true
-    fail_on_errors: true
+plugin: openstack
+expand_hostvars: yes
+fail_on_errors: yes
 '''
 
 import collections