Consistently use JPA 2.1 where available

Boot 1.1 provides Hibernate 4.3.x which is JPA 2.1 compatible but the
platform was providing EclipseLink's JPA 2.0 API. The platform now
provides JPA 2.1 compatible versions of Hibernate (via Boot) and
EclipseLink. OpenJPA remains at JPA 2.0 as no JPA 2.1-compatible version
is available