mon: default ceph_health_raw to json

During the first iteration, the command won't return anything, or can
simply fail and might not return a valid json structure. Ansible will
fail parsing it in the filter `from_json` so let's default that variable
to empty dictionary.

Signed-off-by: Sébastien Han <seb@redhat.com>

roles/ceph-mon/tasks/ceph_keys.yml

@@ -3,7 +3,7 @@
   command: "ceph --cluster {{ cluster }} -n mon. -k /var/lib/ceph/mon/{{ cluster }}-{{ ansible_hostname }}/keyring mon_status --format json"
   register: ceph_health_raw
   until: >
-    (ceph_health_raw.stdout | from_json)['state'] in ['leader', 'peon']
+    (ceph_health_raw.stdout | default({}) | from_json)['state'] in ['leader', 'peon']
   retries: "{{ handler_health_mon_check_retries }}"
   delay: "{{ handler_health_mon_check_delay }}"
   when: