Remove the Rackspace Cloud repo

There's this apt repo on the servers! It has nova-agent in it,
which we don't use - but there it is. Let's remove it, because
that's just really not what we do.

Change-Id: Id1fd4753a96829d3333ece3785246ad9bb141d54

playbooks/roles/base-server/tasks/Debian.yaml

@@ -1,3 +1,7 @@
+- name: Remove Rackspace signing key
+  when: rax_apt_repo_removed.changed
+  command: apt-key del 4096R/CB1EF1DB
+
 - name: Disable install of additional recommends and suggests packages
   copy:
      mode: 0444

playbooks/roles/base-server/tasks/main.yaml

@@ -1,3 +1,9 @@
+- name: Remove Rackspace APT repo
+  file:
+    path: /etc/apt/sources.list.d/ospc.list
+    state: absent
+  register: rax_apt_repo_removed
+
 - name: Install base packages
   package:
     state: present