Do not try to run useradd/groupadd if mash_playbook_uid/mash_playbook_gid explicitly specified

Certain environments (like https://libreelec.tv/) do not have
`useradd`/`groupadd` tools, so it's important to be able to avoid
calling them, especially for no good reason.

roles/mash/playbook_base/tasks/setup_user.yml

@@ -1,24 +1,26 @@
 ---
 
-- name: Ensure mash group is created
+- when: not mash_playbook_uid and not mash_playbook_uid
-  ansible.builtin.group:
+  block:
-    name: "{{ mash_playbook_user_groupname }}"
+    - name: Ensure mash group is created
-    gid: "{{ omit if mash_playbook_gid is none else mash_playbook_gid }}"
+      ansible.builtin.group:
-    state: present
+        name: "{{ mash_playbook_user_groupname }}"
-  register: mash_base_group_result
+        gid: "{{ omit if mash_playbook_gid is none else mash_playbook_gid }}"
+        state: present
+      register: mash_base_group_result
 
-- name: Ensure mash user is created
+    - name: Ensure mash user is created
-  ansible.builtin.user:
+      ansible.builtin.user:
-    name: "{{ mash_playbook_user_username }}"
+        name: "{{ mash_playbook_user_username }}"
-    uid: "{{ omit if mash_playbook_uid is none else mash_playbook_uid }}"
+        uid: "{{ omit if mash_playbook_uid is none else mash_playbook_uid }}"
-    state: present
+        state: present
-    group: "{{ mash_playbook_user_groupname }}"
+        group: "{{ mash_playbook_user_groupname }}"
-    home: "{{ mash_playbook_base_path }}"
+        home: "{{ mash_playbook_base_path }}"
-    create_home: false
+        create_home: false
-    system: true
+        system: true
-  register: mash_base_user_result
+      register: mash_base_user_result
 
-- name: Initialize mash_playbook_uid and mash_playbook_gid
+    - name: Initialize mash_playbook_uid and mash_playbook_gid
-  ansible.builtin.set_fact:
+      ansible.builtin.set_fact:
-    mash_playbook_uid: "{{ mash_base_user_result.uid }}"
+        mash_playbook_uid: "{{ mash_base_user_result.uid }}"
-    mash_playbook_gid: "{{ mash_base_group_result.gid }}"
+        mash_playbook_gid: "{{ mash_base_group_result.gid }}"