nfs: add run once to user creation

The create user call is idempotent but it's also blocking for some
reasons.

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

roles/ceph-nfs/tasks/create_rgw_nfs_user.yml

@@ -7,6 +7,7 @@
 
 - name: create rgw nfs user
   command: "{{ docker_exec_cmd_nfs | default('') }} radosgw-admin --cluster {{ cluster }} user create --uid={{ ceph_nfs_rgw_user }} --display-name='RGW NFS User'"
+  run_once: true
   register: rgwuser
   changed_when: false
   delegate_to: "{{ groups[mon_group_name][0] }}"