ceph-mon: Fix check mode for deploy monitor tasks

Skip the `get initial keyring when it already exists` task when both commands
whose `stdout` output it requires have been skipped (e.g. when running in check
mode).

Signed-off-by: Benoît Knecht <bknecht@protonmail.ch>
(cherry picked from commit 2437f14581)

roles/ceph-mon/tasks/deploy_monitors.yml

@@ -30,6 +30,7 @@
     - name: get initial keyring when it already exists
       set_fact:
         monitor_keyring: "{{ (initial_mon_key.stdout | from_json)[0]['key'] if initial_mon_key is not skipped else monitor_keyring.stdout }}"
+      when: initial_mon_key.stdout|default('')|length > 0 or monitor_keyring is not skipped
 
     - name: create monitor initial keyring
       ceph_key: