Common: Avoid duplicate section in ceph.conf

See:
 - https://github.com/ceph/ceph-ansible/pull/1018#issuecomment-253491094
 - https://github.com/ceph/ceph-ansible/pull/1018#issuecomment-260276588

The workaround here is rendering `ceph_conf_overrides` before passing it
to `config_template` to be sure we won't have a section added twice in
ceph.conf

Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>

roles/ceph-common/tasks/generate_ceph_conf.yml

@@ -10,6 +10,14 @@
     - /etc/ceph/
     - /etc/ceph/ceph.d/
 
+- name: template ceph_conf_overrides
+  local_action: copy content="{{ ceph_conf_overrides }}" dest=/tmp/ceph_conf_overrides_temp
+  run_once: true
+
+- name: get rendered ceph_conf_overrides
+  local_action: set_fact ceph_conf_overrides_rendered="{{ lookup('template', '/tmp/ceph_conf_overrides_temp') | from_yaml }}"
+  run_once: true
+
 - name: "generate ceph configuration file: {{ cluster }}.conf"
   action: config_template
   args:
@@ -18,7 +26,7 @@
     owner: "ceph"
     group: "ceph"
     mode: "0644"
-    config_overrides: "{{ ceph_conf_overrides }}"
+    config_overrides: "{{ ceph_conf_overrides_rendered }}"
     config_type: ini
 
 - name: assemble {{ cluster }}.conf and fragments