Check the Heat purge_deleted crontab on the heat_api_cron container

On the Undercloud, we have 4 Heat api containers:
- heat_api
- heat_api_cron
- heat_api_cfn
- heat_engine

On each container, the heat user has the right job definition in his cron table.
But cronie is only running on the heat_cron_api container.

Change-Id: I6a01a74b15c783add71f83c941141eb3a919211d
Signed-off-by: Gael Chamoulaud <gchamoul@redhat.com>

validations/undercloud-heat-purge-deleted.yaml

@@ -14,7 +14,7 @@
   tasks:
   - name: Get heat crontab
     become: true
-    shell: 'docker exec $(docker ps -q --filter "name=heat" | head -1) crontab -l -u heat |grep -v "^#"'
+    shell: 'docker exec heat_api_cron crontab -l -u heat |grep -v "^#"'
     register: cron_result
     changed_when: False
   - name: Check heat crontab