win_timezone: Add diff support, integration tests (#25284)

* win_timezone: Add diff support, integration tests

This PR includes:

- Diff support
- Returns both previous_timezone and timezone
- Adds integration tests
- More examples
- Improved documentation

* Merged the changes from jborean93's PR

lib/ansible/modules/windows/win_timezone.py

@@ -25,28 +25,51 @@ ANSIBLE_METADATA = {'metadata_version': '1.0',
                     'status': ['preview'],
                     'supported_by': 'community'}
 
-
 DOCUMENTATION = r'''
 ---
 module: win_timezone
-version_added: "2.1"
+version_added: '2.1'
 short_description: Sets Windows machine timezone
 description:
-    - Sets machine time to the specified timezone, the module will check if the provided timezone is supported on the machine.
+- Sets machine time to the specified timezone.
 options:
   timezone:
     description:
-      - Timezone to set to.  Example Central Standard Time
+    - Timezone to set to. Example Central Standard Time
     required: true
-
+notes:
+- The module will check if the provided timezone is supported on the machine.
+- A list of possible timezones is available from C(tzutil.exe /l) and from
+  U(https://msdn.microsoft.com/en-us/library/ms912391.aspx)
+- If running on Server 2008 the hotfix
+  U(https://support.microsoft.com/en-us/help/2556308/tzutil-command-line-tool-is-added-to-windows-vista-and-to-windows-server-2008)
+  needs to be installed to be able to run this module.
 author: Phil Schwartz
 '''
 
-
 EXAMPLES = r'''
-  # Set machine's timezone to Central Standard Time
+- name: Set timezone to 'Romance Standard Time' (GMT+01:00)
   win_timezone:
-    timezone: "Central Standard Time"
+    timezone: Romance Standard Time
+
+- name: Set timezone to 'GMT Standard Time' (GMT)
+  win_timezone:
+    timezone: GMT Standard Time
+
+- name: Set timezone to 'Central Standard Time' (GMT-06:00)
+  win_timezone:
+    timezone: Central Standard Time
 '''
 
-RETURN = r'''# '''
+RETURN = r'''
+previous_timezone:
+    description: The previous timezone if it was changed, otherwise the existing timezone
+    returned: success
+    type: string
+    sample: Central Standard Time
+timezone:
+    description: The current timezone (possibly changed)
+    returned: success
+    type: string
+    sample: Central Standard Time
+'''