Add config option to disable statsd metrics on api vms (#375)

When the newly introduced config option enable_statsd_metrics is set to
false, metrics will be send via prometheus only on api vms. The default
is true, in this case metrics are send via statsd and prometheus.

jobs/cloud_controller_ng/spec

@@ -205,6 +205,7 @@ provides:
   - cc.staging_upload_user
   - cc.statsd_host
   - cc.statsd_port
+  - cc.enable_statsd_metrics
   - cc.system_hostnames
   - cc.tls_port
   - cc.uaa.client_timeout
@@ -980,6 +981,10 @@ properties:
     description: "The port for the statsd server, defaults to the local metron agent"
     default: 8125
 
+  cc.enable_statsd_metrics:
+    description: "Use statsd metrics on api vms."
+    default: true
+
   router.route_services_secret:
     description: "Support for route services is disabled when no value is configured."
     default: ""

jobs/cloud_controller_ng/templates/cloud_controller_ng.yml.erb

@@ -433,6 +433,7 @@ allowed_cors_domains: <%= p("cc.allowed_cors_domains").to_json %>
 
 statsd_host: <%= p("cc.statsd_host") %>
 statsd_port: <%= p("cc.statsd_port") %>
+enable_statsd_metrics: <%= p("cc.enable_statsd_metrics") %>
 
 security_event_logging:
   enabled: <%= p("cc.security_event_logging.enabled") %>