Kryo related fixes

- ProviderIdSerializer fix (ancillary)
- minor improvements
- add test cases

Change-Id: I6d969ac6518c44499f0fac167db4bdf1964f6aaa
diff --git a/core/store/serializers/src/main/java/org/onlab/onos/store/serializers/MastershipTermSerializer.java b/core/store/serializers/src/main/java/org/onlab/onos/store/serializers/MastershipTermSerializer.java
index e4cb999..0ac61a8 100644
--- a/core/store/serializers/src/main/java/org/onlab/onos/store/serializers/MastershipTermSerializer.java
+++ b/core/store/serializers/src/main/java/org/onlab/onos/store/serializers/MastershipTermSerializer.java
@@ -22,7 +22,7 @@
 
     @Override
     public MastershipTerm read(Kryo kryo, Input input, Class<MastershipTerm> type) {
-        final NodeId node = new NodeId(kryo.readObject(input, String.class));
+        final NodeId node = new NodeId(input.readString());
         final int term = input.readInt();
         return MastershipTerm.of(node, term);
     }