timezone: Tidy up docs and arg parsing (#20133)

* Small tweaks for timezone module:

- small textual fixes
- ensure the generated docs list either hwclock or name as required
  by using a non-generated value for required_one_of

* Update docs with the DOCUMENTATION block about either name/hwclock being required

lib/ansible/modules/system/timezone.py

@@ -34,19 +34,20 @@ module: timezone
 short_description: Configure timezone setting
 description:
   - This module configures the timezone setting, both of the system clock
-    and of the hardware clock. I(Currently only Linux platform is supported.)
+    and of the hardware clock. I(Currently only the Linux platform is supported).
     It is recommended to restart C(crond) after changing the timezone,
     otherwise the jobs may run at the wrong time.
     It uses the C(timedatectl) command if available. Otherwise, it edits
     C(/etc/sysconfig/clock) or C(/etc/timezone) for the system clock,
     and uses the C(hwclock) command for the hardware clock.
     If you want to set up the NTP, use M(service) module.
-version_added: "2.2.0"
+version_added: "2.2"
 options:
   name:
     description:
       - Name of the timezone for the system clock.
-        Default is to keep current setting.
+        Default is to keep current setting. B(At least one of name and
+        hwclock are required.)
     required: false
   hwclock:
     description:
@@ -54,6 +55,7 @@ options:
         Default is to keep current setting.
         Note that this option is recommended not to change and may fail
         to configure, especially on virtual environments such as AWS.
+        B(At least one of name and hwclock are required.)
     required: false
     aliases: ['rtc']
 author: "Shinichi TAMURA (@tmshn)"
@@ -233,7 +235,7 @@ class Timezone(object):
 
 
 class SystemdTimezone(Timezone):
-    """This is a Timezone manipulation class systemd-powered Linux.
+    """This is a Timezone manipulation class for systemd-powered Linux.
 
     It uses the `timedatectl` command to check/set all arguments.
     """
@@ -430,13 +432,12 @@ class NosystemdTimezone(Timezone):
 
 def main():
     # Construct 'module' and 'tz'
-    arg_spec = dict(
-        hwclock=dict(choices=['UTC', 'local'], aliases=['rtc']),
-        name   =dict(),
-    )
     module = AnsibleModule(
-        argument_spec=arg_spec,
-        required_one_of=[arg_spec.keys()],
+        argument_spec=dict(
+            hwclock=dict(default=None, choices=['UTC', 'local'], aliases=['rtc']),
+            name=dict(default=None),
+        ),
+        required_one_of=['hwclock', 'name'],
         supports_check_mode=True
     )
     tz = Timezone(module)