Migrate HashedWheelTimer to netty 4

- moved potentially time consuming task to
  shared ScheduledThreadPoolExecutor

Change-Id: I8e77041e0f84bd2bdfd6ae6704f4e39b81c721dd
diff --git a/providers/null/src/main/java/org/onosproject/provider/nil/NullFlowRuleProvider.java b/providers/null/src/main/java/org/onosproject/provider/nil/NullFlowRuleProvider.java
index 8e508d2..98cb848 100644
--- a/providers/null/src/main/java/org/onosproject/provider/nil/NullFlowRuleProvider.java
+++ b/providers/null/src/main/java/org/onosproject/provider/nil/NullFlowRuleProvider.java
@@ -16,9 +16,10 @@
 package org.onosproject.provider.nil;
 
 import com.google.common.collect.Sets;
-import org.jboss.netty.util.HashedWheelTimer;
-import org.jboss.netty.util.Timeout;
-import org.jboss.netty.util.TimerTask;
+
+import io.netty.util.Timeout;
+import io.netty.util.TimerTask;
+
 import org.onlab.util.Timer;
 import org.onosproject.core.ApplicationId;
 import org.onosproject.net.DeviceId;
@@ -52,7 +53,6 @@
 
     private FlowRuleProviderService providerService;
 
-    private HashedWheelTimer timer = Timer.getTimer();
     private Timeout timeout;
 
     /**
@@ -62,7 +62,7 @@
      */
     void start(FlowRuleProviderService providerService) {
         this.providerService = providerService;
-        timeout = timer.newTimeout(new StatisticTask(), 5, TimeUnit.SECONDS);
+        timeout = Timer.newTimeout(new StatisticTask(), 5, TimeUnit.SECONDS);
     }
 
     /**
@@ -126,7 +126,7 @@
                         flowTable.getOrDefault(devId, Collections.emptySet());
                 providerService.pushFlowMetrics(devId, entries);
             }
-            timeout = timer.newTimeout(to.getTask(), 5, TimeUnit.SECONDS);
+            timeout = to.timer().newTimeout(to.task(), 5, TimeUnit.SECONDS);
         }
     }
 }