Avoid lookup of conflicting node with ImportUUIDBehavior.IMPORT_UUID_CREATE_NEW

This issue is related to OAK-1244. The importer will create a new UUID for referenceable nodes when ImportUUIDBehavior.IMPORT_UUID_CREATE_NEW is used. But even with this import behavior, the importer still checks if there is a conflicting node. This is not necessary in this case and should be avoided.