DATAJPA-417 - Upgraded to EclipseLink 2.5.1.

Was able to upgrade to EclipseLink 2.5.1 and re-enable a previously ignored integration tests. However, some of the disabled test cases still fail despite the relevant bug being reported as fixed in 2.5.1.

Turned the workaround in QueryUtils into a TODO for removal as we don't want to strongly force EclipseLink users to upgrade to 2.5.x yet.
DATACMNS-420 - Adapted test cases due to latest changes in Spring Data Commons.