Fix permissions on /etc/{at,cron}.allow

Permissions 640 root:root doesn't allow regular user to read
/etc/{at,cron}.allow files, that changes behavior of at / crontab
commands:

* crontab command can't read /etc/cron.allow and allow any user to modify
  their crontab files.
* at command can't read /etc/at.allow and deny every user.

at / crontab files have SGID bits set, so setting correct group
on /etc/{at,cron}.allow fixes the issue.

Change-Id: I4a3fc8d8e823498d6715e26307424e3065cbd6ca

linux/system/at.sls

@@ -33,8 +33,8 @@ etc_at_allow:
     - template: jinja
     - source: salt://linux/files/cron_users.jinja
     - user: root
-    - group: root
-    - mode: 0600
+    - group: daemon
+    - mode: 0640
     - defaults:
         users: {{ allow_users | yaml }}
     - require:

linux/system/cron.sls

@@ -33,8 +33,8 @@ etc_cron_allow:
     - template: jinja
     - source: salt://linux/files/cron_users.jinja
     - user: root
-    - group: root
-    - mode: 0600
+    - group: crontab
+    - mode: 0640
     - defaults:
         users: {{ allow_users | yaml }}
     - require: