Issue #1972116 by klausi: Add REST test coverage for nodes.

...odules/hal/lib/Drupal/hal/Normalizer/EntityNormalizer.php

core/modules/hal/lib/Drupal/hal/Tests/DenormalizeTest.php

core/modules/node/lib/Drupal/node/NodeStorageController.php

...t/lib/Drupal/rest/Plugin/rest/resource/EntityResource.php

core/modules/rest/lib/Drupal/rest/RequestHandler.php

core/modules/rest/lib/Drupal/rest/Tests/CreateTest.php

core/modules/rest/lib/Drupal/rest/Tests/DeleteTest.php

core/modules/rest/lib/Drupal/rest/Tests/NodeTest.php

core/modules/rest/lib/Drupal/rest/Tests/RESTTestBase.php

core/modules/rest/lib/Drupal/rest/Tests/ReadTest.php

core/modules/rest/lib/Drupal/rest/Tests/UpdateTest.php