Fixes memory leak in InfinispanAsyncMultiMap

Calling ClusterManager.getAsyncMultiMap multiple times can leak memory as the cache listener is still registered.

See vert-x3/issues#316

src/main/java/io/vertx/ext/cluster/infinispan/impl/InfinispanAsyncMultiMap.java

@@ -61,14 +61,16 @@ public class InfinispanAsyncMultiMap<K, V> implements AsyncMultiMap<K, V> {
 
   private final VertxInternal vertx;
   private final Cache<MultiMapKey, Object> cache;
+  private final EntryListener listener;
   private final ConcurrentMap<K, ChoosableSet<V>> nearCache;
   private final TaskQueue taskQueue;
 
   public InfinispanAsyncMultiMap(Vertx vertx, Cache<MultiMapKey, Object> cache) {
     this.vertx = (VertxInternal) vertx;
     this.cache = cache;
     nearCache = new ConcurrentHashMap<>();
-    cache.addListener(new EntryListener());
+    listener = new EntryListener();
+    cache.addListener(listener);
     taskQueue = new TaskQueue();
   }
 
@@ -182,6 +184,11 @@ public void removeAllMatching(Predicate<V> p, Handler<AsyncResult<Void>> complet
 
   }
 
+  @Override
+  public void close() {
+    cache.removeListener(listener);
+  }
+
   public void clearCache() {
     nearCache.clear();
   }