Enabled unattended-upgrades

This works on Debian/Ubuntu only.

There are similar packages for other distributions, but they still
need manual configuration. It seemed better to go for the common
denominator. unattended-upgrades is usually installed by default
anyway, so we are just reinforcing best practices.

roles/common/tasks/main.yml

     - apt-transport-https
     - python-software-properties
 
+- name: Install unattended upgrades (Debian/Ubuntu only)
+  apt: pkg=unattended-upgrades state=installed
+  when: ansible_distribution == 'Debian' or ansible_distribution == 'Ubuntu'
+
 - name: Install ntp
   apt: pkg=ntp state=installed