Add order test to DataModelSerializationRoundtripTest

I'm not very happy with this test. It's very different from the
other tests because it relies on knowledge how the serialized arrays
are constructed. But I think it's good enough. Please keep in mind
that this test is temporary anyway. It will die with the old
serializers.

Change-Id: If0fc89c20b29104438aa28f40ddf5cebe60eb881
Merge "Add order test to DataModelSerializationRoundtripTest"