defaults: add a fact '_current_monitor_address'

So we don't have to loop over `_monitor_addresses` when we need the
monitor address of the current node being played.

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

roles/ceph-defaults/tasks/set_monitor_address.yml

@@ -41,4 +41,10 @@
     - ip_version == 'ipv6'
     - hostvars[item]['monitor_address_block'] | default('subnet')  == 'subnet'
     - hostvars[item]['monitor_address'] | default('0.0.0.0') == '0.0.0.0'
-    - hostvars[item]['monitor_interface'] | default('interface') != 'interface'
+    - hostvars[item]['monitor_interface'] | default('interface') != 'interface'
+
+- name: set_fact _current_monitor_address
+  set_fact:
+    _current_monitor_address: "{{ item.addr }}"
+  with_items: "{{ _monitor_addresses }}"
+  when: inventory_hostname == item.name