apt-repositories: Refactor duplicated code

apt-repositories/tasks/backports.yml

@@ -2,42 +2,20 @@
 
 - name: Backports sources list is installed
   template:
-    src: jessie_backports.list.j2
+    src: '{{ ansible_distribution_release }}_backports.list.j2'
     dest: /etc/apt/sources.list.d/backports.list
     force: yes
     backup: yes
     mode: "640"
   notify: apt update
-  when: ansible_distribution_major_version == '8'
-
-- name: Backports sources list is installed
-  template:
-    src: stretch_backports.list.j2
-    dest: /etc/apt/sources.list.d/backports.list
-    force: yes
-    backup: yes
-    mode: "640"
-  notify: apt update
-  when: ansible_distribution_major_version == '9'
 
 - name: Backports configuration
   copy:
-    src: jessie_backports_preferences
+    src: '{{ ansible_distribution_release }}_backports_preferences'
     dest: /etc/apt/preferences.d/backports
     force: yes
     backup: yes
     mode: "640"
   notify: apt update
-  when: ansible_distribution_major_version == '8'
-
-- name: Backports configuration
-  copy:
-    src: stretch_backports_preferences
-    dest: /etc/apt/preferences.d/backports
-    force: yes
-    backup: yes
-    mode: "640"
-  notify: apt update
-  when: ansible_distribution_major_version == '9'
 
 - meta: flush_handlers