Install gnupg if keys need to be imported

The apt_key module currently requires that gnupg is in place
in order to be able to succesfully import keys.  It is possible
that the system running this role does not have this, so we
should make sure it is installed if we have any keys to install.

Change-Id: Ia5ff4d35dc4faed1fb8dfc6bd32670dae394e5c7

roles/ensure-package-repositories/tasks/Debian.yaml

@@ -1,3 +1,10 @@
+- name: Install GnuPG for apt-key
+  become: true
+  when: repositories_keys | length > 0
+  apt:
+    name: gnupg
+    state: present
+
 - name: Add apt keys
   become: true
   apt_key: