switch2containers: fail if less than 3 monitors

This playbook doesn't support less than 3 monitors present in the inventory.
Just like the rolling_update playbook, let's fail if less than
3 monitors are present.

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=2049132

Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>
(cherry picked from commit f08129e)

infrastructure-playbooks/switch-from-non-containerized-to-containerized-ceph-daemons.yml

@@ -6,14 +6,22 @@
   hosts: localhost
 
   gather_facts: false
-
+  any_errors_fatal: true
   vars_prompt:
     - name: ireallymeanit
       prompt: Are you sure you want to switch from non-containerized to containerized ceph daemons?
       default: 'no'
       private: no
 
   tasks:
+    - import_role:
+        name: ceph-defaults
+
+    - name: fail when less than three monitors
+      fail:
+        msg: "This playbook requires at least three monitors."
+      when: groups[mon_group_name] | length | int < 3
+
     - name: exit playbook, if user did not mean to switch from non-containerized to containerized daemons?
       fail:
         msg: >