Enable proposed-updates repository for some hosts.

This makes stepwise upgrades and testing on parts of the
infrastructure possible.

roles/lmn_network/tasks/main.yml

@@ -19,3 +19,12 @@
     path: /etc/systemd/timesyncd.conf
     insertafter: '^#NTP='
     line: NTP={{ ntp_serv }}
+
+- name: Add proposed-updates repository
+  apt_repository:
+    repo: >
+      deb http://deb.debian.org/debian/ {{ ansible_distribution_release }}-proposed-updates
+      main non-free-firmware
+    state: present
+    update_cache: true
+  when: proposed_updates | default(False)