[JBMAR-160] : SimpleMarshallerTests.testConcurrentHashMap fails on Java 8

The ConcurrentHashMap class has been changed in JDK8.
The fields segments, segmentMask and segmentShift are part of serialPersistentFields.
Solution : Consumption of empty-field stream data in the SerialUnmarshalling, the same way it is done with the RiverUnmarshaller.

[BZ 1074546] : https://bugzilla.redhat.com/show_bug.cgi?id=1074546

Maybe I'm missing something but I don't see the purpose of making this a field.  What does it accomplish?