validate-modules: Fix all system modules (#52384)

This PR includes validate-modules fixes for all system modules.
Except a few that are deliberately implemented like this.

lib/ansible/modules/system/vdo.py

@@ -1,15 +1,11 @@
 #!/usr/bin/python
 
-#
-# Copyright (c) 2018 Red Hat, Inc.
-#
+# Copyright: (c) 2018, Red Hat, Inc.
 # GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
-#
 
 from __future__ import absolute_import, division, print_function
 __metaclass__ = type
 
-
 ANSIBLE_METADATA = {
     'metadata_version': '1.1',
     'status': ['preview'],
@@ -214,6 +210,7 @@ options:
               is only available when creating a new volume, and cannot
               be changed for an existing volume.
         type: str
+        choices: [ dense, sparse ]
     ackthreads:
         description:
             - Specifies the number of threads to use for