Move tasks for all hosts to separate file

When working on !54 it became obvious playbooks could be structured
better in this project.  Therefor we move the tasks supposed to be run
for _all_ hosts to a separate file.  The *main.yml* file should only
import other playbooks from now on, should not define tasks anymore.

all.yml

@@ -0,0 +1,38 @@
+---
+# tasks for all hosts
+
+- hosts: all
+  become: true
+
+  vars:
+    ansible_python_interpreter: /usr/bin/python3
+
+  roles:
+    - role: ansible.timezone
+
+  tasks:
+    - name: Update and clean package cache
+      apt:
+        update_cache: true
+        cache_valid_time: 3600
+        autoclean: true
+      changed_when: false
+
+    - name: Ensure unattended-upgrades is installed and up to date
+      apt:
+        name: unattended-upgrades
+        state: present
+
+    - name: Setup unattended-upgrades
+      include_role:
+        name: ansible-role-unattended-upgrades
+      vars:
+        unattended_origins_patterns:
+          - "origin=Debian,archive=buster-security"
+          - "o=Debian,a=buster-updates"
+        unattended_package_blacklist: [cowsay]
+        unattended_mail: "root"
+
+    - name: Setup users
+      include_role:
+        name: users

main.yml

@@ -1,39 +1,8 @@
 ---
-- hosts: all
+# main playbook aggregating all the other playbooks
-  become: true
 
-  vars:
+- name: Setup for all hosts
-    ansible_python_interpreter: /usr/bin/python3
+  import_playbook: all.yml
-
-  roles:
-    - role: ansible.timezone
-
-  tasks:
-    - name: Update and clean package cache
-      apt:
-        update_cache: true
-        cache_valid_time: 3600
-        autoclean: true
-      changed_when: false
-
-    - name: Ensure unattended-upgrades is installed and up to date
-      apt:
-        name: unattended-upgrades
-        state: present
-
-    - name: Setup unattended-upgrades
-      include_role:
-        name: ansible-role-unattended-upgrades
-      vars:
-        unattended_origins_patterns:
-          - "origin=Debian,archive=buster-security"
-          - "o=Debian,a=buster-updates"
-        unattended_package_blacklist: [cowsay]
-        unattended_mail: "root"
-
-    - name: Setup users
-      include_role:
-        name: users
 
 - name: Specific setup for all proxmox hosts
   import_playbook: proxmox.yml