JCR-2307: ConstraintViolationException expected when a mandatory property is missing and a node with the same name exists

Problem analysis
* When the JCR checks if a mandatory property/sub node exists, it doesn't check for a specific item type such that if we have an existing item with expected name but not the expected type, we won't get the ConstraintViolationException as expected

Fix description
* We now check the name but also the type of the item