fix install-packages playbook, use var in loop and undefined not unset

ansible/00-install-updates.yml

@@ -1,8 +1,8 @@
 ---
 
 - name: Update the system
-  hosts: pibox
   become: true
+  hosts: pibox
   roles:
     - role: apt-update-system
 

ansible/01-install-packages.yml

@@ -1,13 +1,13 @@
 ---
 
-- name: Install Packages
+- name: Remove Packages
   become: true
   hosts: pibox
   tasks:
     - name: Loop over packages_to_install and install them
       ansible.builtin.include_role:
         name: apt-install-package
-      loop: packages_to_install
+      loop: "{{ packages_to_install }}"
       loop_control:
         loop_var: package
 

ansible/roles/apt-install-package/tasks/main.yml

@@ -5,6 +5,6 @@
     update_cache: true
     name: "{{ package }}"
     state: latest
-  failed_when: package is unset
+  failed_when: package is undefined
 
 ...