playbook: fix - use apt_repository to add jessie-backports repo

playbook/roles/vifib-kernel/tasks/main.yml

@@ -5,8 +5,7 @@
     when: ansible_distribution == "Debian" and ansible_distribution_major_version == "9"
 
   - name: Install Debian jessie-backports repository
-    lineinfile: dest='/etc/apt/sources.list' line='deb http://ftp.debian.org/debian jessie-backports main' state=present
-    when: ansible_distribution == "Debian" and ansible_distribution_major_version == "8"
+    apt_repository: repo='deb http://ftp.debian.org/debian jessie-backports main' state=present update_cache=yes
 
   - name: Install kernel 4.9 on debian 8.0
     apt: name=linux-image-4.9.0-0.bpo.5-amd64  state=latest default_release=jessie-backports update_cache=yes
@@ -22,7 +21,6 @@
       - {line: "deb-src http://deb.debian.org/debian jessie main"}
       - {line: "deb http://security.debian.org/ jessie/updates main contrib non-free"}
       - {line: "deb-src http://security.debian.org/ jessie/updates main contrib non-free"}
-      - {line: "deb http://ftp.debian.org/debian jessie-backports main"}
     when: ansible_distribution == "Debian" and ansible_distribution_major_version == "7"
 
   - name: Dist upgrade debian 7 to debian 8