Fix race condition in meter store

Change-Id: I6fd00902f96fc2a0f6d1584a2d5f92360951f9c4
diff --git a/core/api/src/test/java/org/onosproject/store/service/TestDistributedSet.java b/core/api/src/test/java/org/onosproject/store/service/TestDistributedSet.java
index af01cb4..79c108b 100644
--- a/core/api/src/test/java/org/onosproject/store/service/TestDistributedSet.java
+++ b/core/api/src/test/java/org/onosproject/store/service/TestDistributedSet.java
@@ -21,7 +21,6 @@
 import org.onosproject.store.primitives.DefaultDistributedSet;
 
 import java.util.Collection;
-import java.util.HashSet;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Set;
@@ -41,7 +40,7 @@
      * @param setName name to be assigned to this set
      */
     public TestDistributedSet(String setName) {
-        set = new HashSet<>();
+        set = Sets.newConcurrentHashSet();
         listeners = new LinkedList<>();
         this.setName = setName;
     }