Use cron job identifier to be able to update command

Change-Id: Id571945585863a08bd2317b57ecc6123a16e1857

README.rst

           automatic_reboot_time: "02:00"
 
 Linux with cron jobs
+By default it will use name as an identifier, unless identifier key is
+explicitly set or False (then it will use Salt's default behavior which is
+identifier same as command resulting in not being able to change it)
 
 .. code-block:: yaml
 
         job:
           cmd1:
             command: '/cmd/to/run'
+            identifier: cmd1
             enabled: true
             user: 'root'
             hour: 2

linux/system/job.sls

   {%- if job.enabled|default(True) %}
   cron.present:
     - name: {{ job.command }}
+    {%- if job.get('identifier', True) %}
+    - identifier: {{ job.get('identifier', job.get('name', name)) }}
+    {%- endif %}
     - user: {{ job.user|default("root") }}
     {%- if job.minute is defined %}
     - minute: '{{ job.minute }}'
   {%- else %}
   cron.absent:
     - name: {{ job.command }}
+    {%- if job.get('identifier', True) %}
+    - identifier: {{ job.get('identifier', job.get('name', name)) }}
+    {%- endif %}
   {%- endif %}
 
 {%- endfor %}