CacheIgnoreManager unable to persist data

The IgnoredCache test failures are due to a MarshallingException being thrown by the PersistenceMarshallerImpl. This is because no protostream marshaller is able to serialize the ConcurrentHashMap.KeySetView used to store values. Therefore, it's neccesssary to wrap this Set in a Java entity, so that a .proto message and associated marshaller can be generated by ProtoStream.