OMG-587 Errors with embedded list

https://hibernate.atlassian.net/browse/OGM-587

I've moved the test case in core and it showed failure in Neo4j, CouchDB and MongoDB.
The original test included a native query that should have caused a NullPointer but that error has been already fixed by [OGM-590](https://hibernate.atlassian.net/browse/OGM-590).

The test case I've added is the one that generates the Error this issue is about. True the id is "2"  before there was another User created in the original test (the one with id "1"), but we don't need it to throw the exception.