Enabling service's users in /etc/cron.allow

When https://gerrit.mcp.mirantis.net/25051 is merged only
users added to `linux:system:cron` pillar will be allowed
to use crontab tasks.

This commit adds the following users:
* aodh
* cassandra
* ceph
* elasticsearch
* glance
* keystone
* panko
* xtrabackup
* zookeeper

Enable managing cron packages/services and add 'root' user
to both `/etc/at.allow` and `/etc/cron.allow`.

Related-Prod: PROD-22546

Change-Id: Id543d0906842955c5632b1efa6985186afa6c9a9
diff --git a/elasticsearch/server/curator.yml b/elasticsearch/server/curator.yml
index fe7383d..a73ef44 100644
--- a/elasticsearch/server/curator.yml
+++ b/elasticsearch/server/curator.yml
@@ -2,6 +2,12 @@
   _param:
     elasticsearch_curator_indices_pattern: "^(log|notification)-.*$"
     elasticsearch_curator_retention_period: 31
+  linux:
+    system:
+      cron:
+        user:
+          elasticsearch:
+            enabled: true
   elasticsearch:
     server:
       curator: