Only install ansible roles once per run

We're running this per-host delegated to localhost. We only want
to run it once, otherwise we have parallel competing git processes.

Change-Id: I8585a1af2dcc294c0e61fc45d9febb044e42151d

playbooks/roles/install-ansible-roles/tasks/main.yaml

@@ -4,6 +4,7 @@
     dest: '/etc/ansible/roles/{{ ansible_role }}'
     force: yes
   delegate_to: localhost
+  run_once: true
   loop: '{{ ansible_roles }}'
   loop_control:
     loop_var: ansible_role