[docker-orchagent]: ports.json.j2 template fixed (#1177)

* Template generates a correct output now, without excess comma in case
the last port in list has no port speed setting in the redis-db

Signed-off-by: Denis Maslov <Denis.Maslov@cavium.com>

Author: Maslov Denis

dockers/docker-orchagent/ports.json.j2

@@ -1,13 +1,14 @@
 [
 {% if PORT %}
+{% set ns = {'firstPrinted': False} %}
 {% for port in PORT %}
 {% if PORT[port].has_key('speed') %}
-    {
+    {% if ns.firstPrinted %},{% endif %}{
         "PORT_TABLE:{{ port }}": {
             "speed": "{{ PORT[port]['speed'] }}"
         },
         "OP": "SET"
-    }{% if not loop.last %},{% endif %}
+    }{% if ns.update({'firstPrinted': True}) %} {% endif %}
 
 {% endif %}
 {% endfor %}