ClosureCleaner to include reference classes for non-serialization exception

Currently the ClosureCleaner throws exception if {{checkSerializable} is enabled while some object is non-serializable. It includes the non-serializable (nested) object in the exception in the exception message.

However, when the user job program gets more complex pulling multiple operators each of which pulls multiple 3rd party libraries, it is unclear how the non-serializable object is referenced as some of those objects could be nested in multiple levels. For example, following exception is not straightforward where to check:

org.apache.flink.api.common.InvalidProgramException: java.lang.Object@528c868 is not serializable. 

It would be nice to include the reference stack in the exception message, as following:

org.apache.flink.api.common.InvalidProgramException: java.lang.Object@72437d8d is not serializable. Referenced via [class com.mycompany.myapp.ComplexMap, class com.mycompany.myapp.LocalMap, class com.yourcompany.yourapp.YourPojo, class com.hercompany.herapp.Random, class java.lang.Object] ...