roles/common: use Ansible timezone module

No need to use a command for that. The module does it better because
it doesn't register a change unless the timezone changes.

roles/common/tasks/ntp.yml

@@ -4,8 +4,11 @@
 # client.
 
 - name: Set timezone
-  when: timezone is defined and ansible_service_mgr == 'systemd'
-  command: /usr/bin/timedatectl set-timezone {{ timezone }}
+  when:
+    - timezone is defined
+    - ansible_service_mgr == 'systemd'
+  community.general.timezone:
+    name: "{{ timezone }}"
   tags: timezone
 
 # Apparently some cloud images don't have this installed by default. From what