Modularize spring-boot-test

[philwebb]

The test modules know about everything at the moment and we'd like to modularize them

[wilkinsona]

As part of this, we may want to consider the location/name of @DataJpaTest. It's in org.springframework.boot.test.autoconfigure.orm.jpa at the moment but it auto-configures Spring Data JPA repositories. Perhaps it should move to a data.jpa package?