Avoid ignore_errors on Set ephemeral device by label

Avoids confusing output that looks like:
primary | ERROR: Ignoring Errors

Return code different than zero is normal and should not fail
that task, using failed_when does avoid displaying the task
as a failure when the rc is not zero (most builds).

Change-Id: I00e70c65c73880281f13d8bf92c5779814e57837

roles/configure-swap/tasks/main.yaml

@@ -19,8 +19,8 @@
     - name: Get ephemeral0 device node
       command: /sbin/blkid -L ephemeral0
       register: ephemeral0
-      # If this doesn't exist, returns !0
-      ignore_errors: yes
+      # rc !=0 is expected
+      failed_when: False
       changed_when: False
 
     - name: Set ephemeral device if LABEL exists