validate: fail in check_devices at the right task

see https://bugzilla.redhat.com/show_bug.cgi?id=1648168#c17 for details.

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1648168#c17

Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>
(cherry picked from commit 771648304d)

roles/ceph-validate/tasks/check_devices.yml

@@ -1,14 +1,17 @@
 ---
-- name: validate devices is actually a device
+- name: devices validation
+  when: devices is defined
+  block:
+    - name: get devices information
       parted:
         device: "{{ item }}"
         unit: MiB
       register: devices_parted
+      failed_when: False
       with_items: "{{ devices }}"
 
     - name: fail if one of the devices is not a device
       fail:
         msg: "{{ item }} is not a block special file!"
-  when:
-    - item.failed
+      when: item.rc is defined
       with_items: "{{ devices_parted.results }}"