Add HashMultiset Catalyst serializer - used in ConsistentMultimap.

Plus catch serialization exceptions during message receive, simplify
implementation of HashMultisetValueCollector, other minor cleanups.

Change-Id: Ia50b39205a8241f456ee90ef765a8e478da868ab
diff --git a/core/store/serializers/src/main/java/org/onosproject/store/serializers/KryoNamespaces.java b/core/store/serializers/src/main/java/org/onosproject/store/serializers/KryoNamespaces.java
index 4db7a11..c086cb8 100644
--- a/core/store/serializers/src/main/java/org/onosproject/store/serializers/KryoNamespaces.java
+++ b/core/store/serializers/src/main/java/org/onosproject/store/serializers/KryoNamespaces.java
@@ -15,6 +15,7 @@
  */
 package org.onosproject.store.serializers;
 
+import com.google.common.collect.HashMultiset;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
@@ -274,6 +275,7 @@
                       HashSet.class,
                       LinkedHashSet.class
             )
+            .register(HashMultiset.class)
             .register(Maps.immutableEntry("a", "b").getClass())
             .register(new ArraysAsListSerializer(), Arrays.asList().getClass())
             .register(Collections.singletonList(1).getClass())