Ensure hydrator from metadata map is used

- In the case when no default hydrator is present, ensure that any
  hydrator set in the metadata map is used.
Better test for metadata hydrators

- The issue is more easily noticed on objects with protected properties.
  Changed the resource used to have those, and use an alternate
  hydrator. Tests now fail before the change to HalLinks.
Merge branch 'hotfix/metadata-hydrator'