Fix retrievement keyrings from files

With [1] usage of custom owner/group has been introduced. It
converted client to be a list of mappings but it was missed in 1 place.

[1] fdd2aaa00b
Closes-Bug: #2024339

Change-Id: Icfc16ca25f0b6b45a0de0bcdf4eac71ab302a120

tasks/ceph_get_keyrings_from_files.yml

@@ -21,7 +21,7 @@
       {% set _keys = {} %}
       {% for client in ceph_client_filtered_clients %}
       {%   set _ = _keys.update({
-              client: lookup('file', ceph_keyrings_dir ~ '/' ~ client['name'] ~ '.keyring')
+              client['name']: lookup('file', ceph_keyrings_dir ~ '/' ~ client['name'] ~ '.keyring')
           })
       %}
       {% endfor %}