roles/common: Don't configure apt sources on ARM

I was using this on Ubuntu, but might as well bring it here too so
that I can run Debian on Scaleway's ARM instances, for example.

roles/common/tasks/packages_Debian.yml

@@ -3,6 +3,7 @@
 - block:
   - name: Configure apt mirror
     template: src=sources.list.j2 dest=/etc/apt/sources.list owner=root group=root mode=0644
+    when: ansible_architecture != 'armv7l'
 
   - name: Set fact for base packages
     set_fact: