start ns_stats_event earler

So that ns_heart that does gen_event:call there doesn't get noproc
(via failover_safeness_level:get_value). That early call will fail
anyways due to failover_safeness_level not being installed, but that
error is handled and unknown is expectedly returned.

Change-Id: I5d34eab8b696f1a586aaa8d29d529bf9b7006810
Reviewed-on: http://review.couchbase.org/12903
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>

src/ns_server_sup.erl

@@ -75,6 +75,9 @@ child_specs() ->
      {ns_mail_sup, {ns_mail_sup, start_link, []},
       permanent, infinity, supervisor, [ns_mail_sup]},
 
+     {ns_stats_event, {gen_event, start_link, [{local, ns_stats_event}]},
+      permanent, 1000, worker, dynamic},
+
      {ns_heart, {ns_heart, start_link, []},
       permanent, 1000, worker, [ns_heart]},
 
@@ -89,9 +92,6 @@ child_specs() ->
       permanent, 60000, worker,
       [ns_port_sup]},
 
-     {ns_stats_event, {gen_event, start_link, [{local, ns_stats_event}]},
-      permanent, 1000, worker, dynamic},
-
      {ns_bucket_worker, {work_queue, start_link, [ns_bucket_worker]},
       permanent, 1000, worker, [work_queue]},