Allow ceph-mon systemd overrides to be specified

ceph-mon can fail to start under certain circumstances (for example,
when running in a container) because the default systemd service
configuration causes namespace issues.

To work around this we can override the system service settings by
placing an overrides file in the ceph-mon@.service.d directory. This can
be generic so as to allow any potential changes required to the ceph-mon
service file.

tasks/start_monitor.yml

@@ -1,4 +1,14 @@
 ---
+- name: add ceph-mon systemd service overrides
+  config_template:
+    src: "ceph-mon.service.d-overrides.j2"
+    dest: "/etc/systemd/system/ceph-mon@.service.d/ceph-mon-systemd-overrides.conf"
+    config_overrides: "{{ ceph_mon_systemd_overrides }}"
+    config_type: "ini"
+  when:
+    - ceph_mon_systemd_overrides is defined
+    - ansible_service_mgr == 'systemd'
+
 - name: start the monitor service
   service:
     name: ceph-mon@{{ monitor_name }}

templates/ceph-mon.service.d-overrides.j2

@@ -0,0 +1,2 @@
+# {{ ansible_managed }}
+[Service]