Roundtrip tests for Lib\Serializers vs. DataModelSerialization

This is still missing the options the new serializer needs to
support. But I would like to do this in separate patches.

Change-Id: I10ed6aef22f48f1a44efe9e79cc2d3a47889ca91
Merge "Roundtrip tests for Lib\Serializers vs. DataModelSerialization"