Cleaning-up shared executors use of metrics service.

Change-Id: I4293df87cd46e9f22cbdf03cfbced9a21ba85de7
diff --git a/core/net/src/main/java/org/onosproject/core/impl/CoreManager.java b/core/net/src/main/java/org/onosproject/core/impl/CoreManager.java
index a8405dd..2b44b2a 100644
--- a/core/net/src/main/java/org/onosproject/core/impl/CoreManager.java
+++ b/core/net/src/main/java/org/onosproject/core/impl/CoreManager.java
@@ -101,7 +101,7 @@
 
 
     @Activate
-    public void activate() {
+    protected void activate() {
         registerApplication(CORE_APP_NAME);
         cfgService.registerProperties(getClass());
         try {
@@ -117,7 +117,7 @@
     }
 
     @Deactivate
-    public void deactivate() {
+    protected void deactivate() {
         cfgService.unregisterProperties(getClass(), false);
         SharedExecutors.shutdown();
     }
@@ -171,7 +171,7 @@
 
 
     @Modified
-    public void modified(ComponentContext context) {
+    protected void modified(ComponentContext context) {
         Dictionary<?, ?> properties = context.getProperties();
         Integer poolSize = Tools.getIntegerProperty(properties, "sharedThreadPoolSize");
 
@@ -193,7 +193,7 @@
         Boolean performanceCheck = Tools.isPropertyEnabled(properties, "sharedThreadPerformanceCheck");
         if (performanceCheck != null) {
             calculatePoolPerformance = performanceCheck;
-            SharedExecutors.setCalculatePoolPerformance(calculatePoolPerformance, metricsService);
+            SharedExecutors.setMetricsService(calculatePoolPerformance ? metricsService : null);
         }
 
         log.info("Settings: sharedThreadPoolSize={}, maxEventTimeLimit={}, calculatePoolPerformance={}",