Check the keystone token flush on the keystone_cron container

On the Undercloud, we have two keystone container (keystone and keystone_cron).
On both container, the keystone user has the right job definition in the cron
table. But cronie is only running on the keystone_cron container.

Change-Id: I326045519d4daf6719b27c51b4cb575bb4b5474c
Signed-off-by: Gael Chamoulaud <gchamoul@redhat.com>

validations/undercloud-tokenflush.yaml

@@ -13,7 +13,7 @@
   tasks:
   - name: Get keystone crontab
     become: true
-    shell: 'docker exec $(docker ps -q --filter "name=keystone" | head -1) crontab -l -u keystone |grep -v "^#"'
+    shell: 'docker exec keystone_cron crontab -l -u keystone |grep -v "^#"'
     register: cron_result
     changed_when: False
   -