update: skip mds deactivation when no mds in inventory

Let's skip this part of the code if there's no mds node in the
inventory.

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

infrastructure-playbooks/rolling_update.yml

@@ -541,6 +541,9 @@
   hosts: "{{ groups[mon_group_name|default('mons')][0] }}"
   become: true
   tasks:
+    - name: deactivate all mds rank > 0
+      when: groups.get(mds_group_name, []) | length > 1
+      block:
         - import_role:
             name: ceph-defaults
         - import_role:
@@ -614,7 +617,7 @@
 - name: upgrade active mds
   vars:
     upgrade_ceph_packages: True
-  hosts: active_mdss
+  hosts: active_mdss | default([])
   become: true
   tasks:
     - import_role: