ErrorInfo needs to hold Exception as SerializedThrowable

MemoryArchivist holding on to last thrown exception prevents the user code classloader from being garbage collected.

MemoryArchivist holds on to any number of ArchivedExecutionGraph's. These ArchivedExecutionGraph instances contain a failureCause field of type ErrorInfo that wrap the exception in case one was thrown to terminate the job

This exception class will more often than not have been loaded by a user code classloader, and as long as the MemoryArchivist holds on to this exception, the JVM won't be able to reclaim the resources held by this classloader