Don't fail ironic upgrade if xinetd isn't present

When upgrading from Rocky to master in CI, we don't seem to have
xinetd present in the overcloud, and attempting to restart it fails
the upgrade. Check if it's running before trying to restart it.

Change-Id: I9f45340cf6caf7811aa03a1b2aa16eec599d4faa
Closes-Bug: #1792527

docker/services/ironic-pxe.yaml

@@ -95,10 +95,15 @@ outputs:
               file:
                 path: /etc/xinetd.d/tftp
                 state: absent
+            - name: query if xinetd is active
+              failed_when: false
+              shell: systemctl is-active xinetd
+              register: xinetd_active_result
             - name: restart xinetd in order to free tftp port
               service:
                 name: xinetd
                 state: restarted
+              when: xinetd_active_result.rc == 0
         - when: step|int == 3
           block:
             - name: Set fact for removal of tftp-server package